SLS

Retail investors are awaiting clarity on Sellas’ cash position, quiet period, and Regal trial event count. The Regal trial remained two events short of the 80 deaths required to trigger its final overall survival analysis. Sellas estimated $138.3 million in cash despite losing its $13 million arbitration claim against 3D Medicines. Shares of Sellas Life Sciences (SLS) rebounded over 1% in premarket trading on Tuesday after its worst session in nearly three weeks as investors looked to an anticipated second-quarter (Q2) update for clarity on the company’s cash position and key Phase 3 Regal trial. SLS stock fell 8% on Monday to close at $11.04 before edging 0.3% higher in extended trading. See what 10M+ investors are talking about. Get the Stocktwits Daily Rip for what retail is watching right now, free to your inbox On Stocktwits, retail sentiment for SLS slipped to ‘bearish’ from ‘neutral’ levels a day ago amid a 238% jump in 24-hour message volumes. One user said an all-at-once update covering those issues “could be a huge and very special day,” while another predicted that investors would receive a 10-Q this week, potentially accompanied by an 8-K or LinkedIn post from CEO Angelos Stergiou. Others questioned the company’s quiet period. “Why are they in a QP?” one trader asked, speculating that it could indicate access to data or buyout discussions. Another user noted that nearly four weeks had passed since Stergiou said Regal was “approaching [the] 80th event threshold” and suggested that final-analysis topline data could be “impending.” Still, retail expectations carry downside risk. One trader warned that releasing Q2 results without clarifying the event count “will only drive the SP down,” adding that “impatience is setting in.” Sellas is not expected to report quarterly revenue, according to Koyfin. Wall Street forecasts a GAAP loss of $0.04 per share, narrowing from $0.05 previously, and an operating loss of $9.08 million versus $9.25 million in the prior period. The two analysts covering SLS rate it a “Strong Buy,” with price targets of $25 and $30. The $27.50 average target implies about 149% upside from current levels. Regal is evaluating Sellas’ Galinpepimut-S (GPS) as maintenance therapy for acute myeloid leukemia (AML) patients who achieved complete remission following second-line treatment. The event-driven study had recorded 78 of the 80 deaths required to trigger its final analysis, leaving it two events short at the company’s last update. Stergiou called the slower-than-expected event accumulation as encouraging because the primary endpoint is overall survival. Sellas has said the trial would be considered successful if GPS delivers a median overall survival of 12.6 months, compared with eight months under standard treatment. Sellas recently estimated that it held $138.3 million in cash and cash equivalents as of June 30, up from $107.1 million at the end of the first quarter after receiving $28.7 million through warrant exercises in April and May. The stronger liquidity position followed an arbitration setback involving Chinese biotechnology company 3D Medicines. The sole arbitrator dismissed Sellas’ claims for $13 million in disputed GPS milestone payments and ordered it to contribute about $1 million toward 3D Medicines’ legal costs. The broader partnership remains intact, with 3D Medicines continuing to develop and commercialize GPS in Greater China. The agreement carries up to $191.5 million in potential future milestone payments, including the disputed $13 million. SLS stock has surged 599% over the past year. For updates and corrections, email newsroom[at]stocktwits[dot]com. Read Next: SpaceX Stock Slips Overnight After 3-Day Rally — Here's Why Ron Baron Sees 40x Upside And ‘Hundreds Of Billions’ In Gains Deepti Sri has no position in any of the stocks mentioned in this article. StockTwits' news team content is for informational purposes only and is not intended as investment advice. For more, see our editorial policy. This article was originally published on StockTwits. Related: INTS Q2 2026 Earnings Summary BSIN Q2 2026 Earnings Summary JBL Stock Jumps 6% After UBS Upgrade — How Amazon, Meta, Google Could Power Jabil’s AI Growth

- Final Analysis of Phase 3 REGAL Trial of Galinpepimut-S (GPS) in Acute Myeloid Leukemia to be Conducted Following the 80th Event - - 28 Patients Enrolled in Phase 2 Trial of SLS009 in Newly Diagnosed First-Line AML; Topline Data Expected in Q4 2026 - - Strong Preclinical Indications of Efficacy of SLS009 in Advanced Pancreatic Cancer Resistant to RAS inhibitors, Clinical Development Preparations Ongoing - - $138.3 Million in Cash and Cash Equivalents as of June 30, 2026 - NEW YORK, Aug. 11, 2026 (GLOBE NEWSWIRE) -- SELLAS Life Sciences Group, Inc. (NASDAQ: SLS) (“SELLAS’’ or the “Company”), a late-stage clinical biopharmaceutical company focused on the development of novel therapies for a broad range of cancer indications, today reported financial results for the second quarter ended June 30, 2026, and provided a corporate update. “The second quarter was an important period of execution for SELLAS as we continued to advance both of our lead clinical programs, GPS and SLS009,” said Angelos Stergiou, MD, ScD h.c., President and Chief Executive Officer of SELLAS. “For GPS, we are approaching the pre-specified 80th event in the Phase 3 REGAL trial marking a critical step toward the final efficacy analysis and, if successful, a potential BLA submission to the FDA. At the same time, we are making meaningful progress with SLS009 in our ongoing Phase 2 frontline AML study, where dosing continues and enrollment is tracking ahead of industry standards, with topline data expected in the fourth quarter of 2026. In addition, we have obtained promising results from preclinical studies in pancreatic ductal adenocarcinoma (PDAC) and intend to support clinical development at a top-tier academic institution. Together, these programs reflect our commitment to developing differentiated therapies that may address significant unmet needs for patients with AML and support meaningful long-term value creation for SELLAS.” Recent Corporate Highlights: Phase 3 REGAL Trial of GPS: Ongoing Phase 3 trial in AML patients who have achieved complete remission following second-line salvage therapy. The Company will announce when the required pre-specified 80th event occurs, which will trigger the customary database lock, blinded data review procedures before statistical analysis, unblinding, and disclosure of topline results. Ongoing dosing of SLS009 in earlier-line AML: 28 patients have been enrolled, and enrollment and dosing continue in the ongoing 80-patient Phase 2 trial in newly diagnosed AML patients, including those who become refractory early to AZA/VEN treatment identified through extensive transcriptomics, genomics, and proteomics models. Topline data expected in Q4 2026. Additional information about the trial can be found at clinicaltrials.gov (NCT04588922). Potential expansion of SLS009 into solid cancers: SLS009 has demonstrated the ability to act as a single agent in PDAC cells largely resistant to leading RAS inhibitors and synergize with the RAS inhibition mechanism of action. The data from these preclinical experiments are expected to be presented at an upcoming medical conference. Financial Results for the Second Quarter 2026: Research and Development Expenses: Research and development expenses for the quarter ended June 30, 2026, were $6.3 million, compared to $3.9 million for the same period in 2025. Research and development expenses in the first half of 2026 were $11.4 million compared to $7.1 million for the same period in 2025. The increase was primarily due to increases in manufacturing costs, clinical and regulatory consulting, and clinical trial expenses in preparation for a potential Biologics License Application (BLA) for GPS following the final analysis of the REGAL study. General and Administrative Expenses: General and administrative expenses for the second quarter of 2026 were $4.4 million, as compared to $3.0 million for the same period in 2025. General and administrative expenses in the first half of 2026 were $8.5 million compared to $5.9 million for the same period in 2025.  The increase was primarily due to increases in professional fees and non-cash stock-based compensation. Net Loss: The net loss was $9.6 million for the second quarter of 2026, or a basic and diluted loss per share of $0.05, as compared to a net loss of $6.6 million for the second quarter of 2025, or a basic and diluted loss per share of $0.07. The net loss was $18.0 million for the first half of 2026, or a basic and diluted loss per share of $0.10, as compared to a net loss of $12.4 million for the second quarter of 2025, or a basic and diluted loss per share of $0.13. Cash Position: As of June 30, 2026, cash and cash equivalents totaled approximately $138.3 million. About SELLAS Life Sciences Group, Inc. SELLAS is a late-stage clinical biopharmaceutical company focused on the development of novel therapeutics for a broad range of cancer indications. SELLAS’ lead product candidate, GPS, is licensed from Memorial Sloan Kettering Cancer Center and targets the WT1 protein, which is present in an array of tumor types. GPS has the potential as a monotherapy and combination with other therapies to address a broad spectrum of hematologic malignancies and solid tumor indications. The Company is also developing SLS009 (tambiciclib) - potentially the first and best-in-class differentiated small molecule CDK9 inhibitor with reduced toxicity and increased potency compared to other CDK9 inhibitors. Data suggests that SLS009 demonstrated a high response rate in AML patients with unfavorable prognostic factors including ASXL1 mutation, commonly associated with poor prognosis in various myeloid diseases. For more information on SELLAS, please visit www.sellaslifesciences.com. Forward-Looking Statements This press release contains forward-looking statements. All statements other than statements of historical facts are “forward-looking statements,” including those relating to future events. In some cases, forward-looking statements can be identified by terminology such as “plan,” “expect,” “anticipate,” “may,” “might,” “will,” “should,” “project,” “believe,” “estimate,” “predict,” “potential,” “intend,” or “continue” and other words or terms of similar meaning. These statements include, without limitation, statements related to the GPS clinical development program, including the REGAL study and the timing of future milestones related thereto. These forward-looking statements are based on current plans, objectives, estimates, expectations, and intentions, and inherently involve significant risks and uncertainties. Actual results and the timing of events could differ materially from those anticipated in such forward-looking statements as a result of these risks and uncertainties, which include, without limitation, risks and uncertainties with oncology product development and clinical success thereof, the uncertainty of regulatory approval, and other risks and uncertainties affecting SELLAS and its development programs as set forth under the caption “Risk Factors” in SELLAS’ Annual Report on Form 10-K filed on March 19, 2026 and in its other SEC filings. Other risks and uncertainties of which SELLAS is not currently aware may also affect SELLAS’ forward-looking statements and may cause actual results and the timing of events to differ materially from those anticipated. The forward-looking statements herein are made only as of the date hereof. SELLAS undertakes no obligation to update or supplement any forward-looking statements to reflect actual results, new information, future events, changes in its expectations, or other circumstances that exist after the date as of which the forward-looking statements were made. Investor Contact John FrauncesManaging DirectorLifeSci Advisors, [email protected]

– Contract Research Organization for the Pivotal Phase 3 REGAL Trial of Galinpepimut-S (GPS) in Acute Myeloid Leukemia (AML) Informed the Company that 78 Events have Occurred in the Trial as of May 11, 2026; SELLAS Remains Blinded to Trial Outcomes – – Final Analysis of REGAL Trial of GPS in AML to be Conducted Following the 80th Event – – Ongoing Dosing of Patients in Phase 2 Trial of SLS009 in Newly Diagnosed First Line AML – – $107.1 Million in Cash and Cash Equivalents as of March 31, 2026; Additional $7.5 Million in Proceeds Received in Q2 2026 to Date through Warrant Exercises – NEW YORK, May 12, 2026 (GLOBE NEWSWIRE) -- SELLAS Life Sciences Group, Inc. (NASDAQ: SLS) (“SELLAS’’ or the “Company”), a late-stage clinical biopharmaceutical company focused on the development of novel therapies for a broad range of cancer indications, today reported financial results for the first quarter ended March 31, 2026, and provided a corporate update. “The first quarter of 2026 marked an important period for SELLAS as we continued to execute across our clinical programs while preparing for the anticipated pivotal Phase 3 REGAL trial data readout,” said Angelos Stergiou, MD, ScD h.c., President and Chief Executive Officer of SELLAS. “We are grateful for the ongoing commitment of the patients, caregivers, and investigators participating in the pivotal Phase 3 REGAL trial and we believe that the upcoming results, triggered by reaching the pre-specified 80th event, will be an important milestone for the Company.” “In parallel, we are generating increasingly compelling data with SLS009, including recent preclinical findings presented at AACR demonstrating potent, mechanistically driven activity in AML through suppression of key survival pathways such as MCL-1 and induction of apoptosis, including in high-risk genetic subtypes like TP53 and ASXL1 mutations. Importantly, we have begun dosing patients in our Phase 2 study of SLS009 in newly diagnosed, first-line AML, targeting high-risk populations unlikely to benefit from standard therapies, including venetoclax. With REGAL approaching its critical readout and SLS009 advancing across clinical and translational fronts, we believe that SELLAS is entering an exciting time with multiple, high-value potential catalysts that could transform the AML treatment landscape.” Recent Corporate Highlights: Phase 3 REGAL Trial of GPS: Ongoing Phase 3 REGAL trial evaluating GPS in AML patients who have achieved complete remission following second-line salvage therapy. Reaching the required pre-specified 80th event (death) will trigger the customary database lock, blinded data review procedures prior to statistical analysis, unblinding, and disclosure of topline results. As of May 11, 2026, 78 events have occurred and SELLAS will provide an update and announce when the 80th event has been reached. Ongoing dosing of SLS009 in earlier-line AML: SELLAS has initiated an 80-patient Phase 2 trial in newly diagnosed AML patients, including those who become refractory early to AZA/VEN treatment identified through extensive transcriptomics, genomics, and proteomics models. The topline data are expected in Q4 2026. Additional information about the trial can be found at clinicaltrials.gov (NCT04588922). Preclinical Data on SLS009 in AML Presented at the 2026 American Association for Cancer Research (AACR): The data show that SLS009 induces apoptosis in AML cell lines, including those harboring high-risk ASXL1 and TP53 mutations. Pharmacodynamic changes were observed as early as 8 hours after treatment and became more pronounced over time, with reductions in MCL-1 and survivin levels that correlated with increased apoptosis. The poster, entitled “Tambiciclib (SLS009), a CDK9 inhibitor, promotes apoptosis and suppresses MCL-1 levels in AML cell lines,” can be viewed here. At-the-Market (ATM) Offering: SELLAS established an ATM equity offering under its S-3ASR shelf registration, providing the Company with the ability to raise up to $150 million in capital over time. The facility, to be utilized through TD Cowen, enables flexible and opportunistic access to the equity markets. The Company has not sold any shares of common stock through its ATM to date. Financial Results for the First Quarter 2026: Research and Development Expenses: Research and development expenses for the quarter ended March 31, 2026, were $5.1 million, compared to $3.2 million for the same period in 2025. The increase was primarily due to increases in manufacturing costs, clinical and regulatory consulting, and clinical trial expenses in preparation for a potential Biologics License Application for GPS following the final analysis of the REGAL study. General and Administrative Expenses: General and administrative expenses for the first quarter of 2026 were $4.1 million, as compared to $2.9 million for the same period in 2025. The increase was primarily due to increases in professional fees, consulting and public company costs, and non-cash stock-based compensation. Net Loss: The net loss was $8.4 million for the first quarter of 2026, or a basic and diluted loss per share of $0.05, as compared to a net loss of $5.8 million for the first quarter of 2025, or a basic and diluted loss per share of $0.07. Cash Position: As of March 31, 2026, cash and cash equivalents totaled approximately $107.1 million. Subsequent to March 31, 2026, the Company received an additional $7.5 million in proceeds from the exercise of previously outstanding warrants. About SELLAS Life Sciences Group, Inc. SELLAS is a late-stage clinical biopharmaceutical company focused on the development of novel therapeutics for a broad range of cancer indications. SELLAS’ lead product candidate, GPS, is licensed from Memorial Sloan Kettering Cancer Center and targets the WT1 protein, which is present in an array of tumor types. GPS has the potential as a monotherapy and combination with other therapies to address a broad spectrum of hematologic malignancies and solid tumor indications. The Company is also developing SLS009 (tambiciclib) - potentially the first and best-in-class differentiated small molecule CDK9 inhibitor with reduced toxicity and increased potency compared to other CDK9 inhibitors. Data suggests that SLS009 demonstrated a high response rate in AML patients with unfavorable prognostic factors including ASXL1 mutation, commonly associated with poor prognosis in various myeloid diseases. For more information on SELLAS, please visit www.sellaslifesciences.com. Forward-Looking Statements This press release contains forward-looking statements. All statements other than statements of historical facts are “forward-looking statements,” including those relating to future events. In some cases, forward-looking statements can be identified by terminology such as “plan,” “expect,” “anticipate,” “may,” “might,” “will,” “should,” “project,” “believe,” “estimate,” “predict,” “potential,” “intend,” or “continue” and other words or terms of similar meaning. These statements include, without limitation, statements related to the GPS clinical development program, including the REGAL study and the timing of future milestones related thereto. These forward-looking statements are based on current plans, objectives, estimates, expectations, and intentions, and inherently involve significant risks and uncertainties. Actual results and the timing of events could differ materially from those anticipated in such forward-looking statements as a result of these risks and uncertainties, which include, without limitation, risks and uncertainties with oncology product development and clinical success thereof, the uncertainty of regulatory approval, and other risks and uncertainties affecting SELLAS and its development programs as set forth under the caption “Risk Factors” in SELLAS’ Annual Report on Form 10-K filed on March 19, 2026 and in its other SEC filings. Other risks and uncertainties of which SELLAS is not currently aware may also affect SELLAS’ forward-looking statements and may cause actual results and the timing of events to differ materially from those anticipated. The forward-looking statements herein are made only as of the date hereof. SELLAS undertakes no obligation to update or supplement any forward-looking statements to reflect actual results, new information, future events, changes in its expectations, or other circumstances that exist after the date as of which the forward-looking statements were made. Investor Contact John Fraunces Managing Director LifeSci Advisors, LLC [email protected]

– Continued Advancement of Pivotal Phase 3 REGAL Trial of Galinpepimut-S (GPS) in Acute Myeloid Leukemia (AML) - Final Analysis upon Reaching 80 Events – – First Patient Dosed in Phase 2 Trial of SLS009 in Newly Diagnosed First Line AML – – Reported Positive Phase 2 Data of SLS009 in Relapsed/Refractory (r/r) AML at ASH 2025 – – $71.8 Million in Cash and Cash Equivalents as of December 31, 2025; Additional $42.6 Million in Proceeds Received in Q1 2026 to Date Through Warrant Exercises – NEW YORK, March 19, 2026 (GLOBE NEWSWIRE) -- SELLAS Life Sciences Group, Inc. (NASDAQ: SLS) (“SELLAS’’ or the “Company”), a late-stage clinical biopharmaceutical company focused on the development of novel therapies for a broad range of cancer indications, today reported financial results for the full year ended December 31, 2025, and provided a corporate update. “Based upon continued progress in our GPS and SLS009 clinical programs in AML, we believe 2026 is shaping up to be a pivotal year for SELLAS,” said Angelos Stergiou, MD, ScD h.c., President and Chief Executive Officer of SELLAS. “We are advancing toward the final analysis of our Phase 3 REGAL trial evaluating GPS in AML patients who have achieved complete remission following second-line salvage therapy. Once we reach the required pre-specified 80th event, which will be announced, we will proceed with the necessary procedures towards database lock completion, statistical analysis, unblinding, and disclosure of topline results. If positive, REGAL could position GPS as a first- and best-in-class immunotherapeutic option in this AML population and serve as a significant value-inflection point for SELLAS.” Dr. Stergiou continued, “We also continue to make significant progress in our SLS009 clinical program for AML. Following the positive Phase 2 results of SLS009 in r/r AML presented at ASH, particularly in high-risk molecular subtypes, we have now dosed the first patient in the expansion cohort, which is evaluating SLS009 in newly diagnosed, first-line AML patients. Additionally, our preclinical data presented at ESMO in T-PLL demonstrated a statistically significant survival benefit of SLS009 both as monotherapy and in combination with venetoclax in a patient-derived xenograft model, further supporting the breadth of the CKD9 inhibition strategy. With a catalyst rich outlook, continued clinical execution, our strongest financial position in history, and expansion into earlier treatment settings, we look forward to an important year ahead.” Recent Corporate Highlights: European Collaboration to Advance SLS009 Clinical Program: In January 2026, SELLAS entered into a strategic collaboration with IMPACT-AML to expand SLS009 clinical program in Europe. Under the agreement, IMPACT-AML’s STREAM clinical network will conduct a study of SLS009 in combination with AZA/VEN in newly diagnosed AML patients. The enrollment of approximately 40 patients in Europe is anticipated in Q2 2026. Phase 3 REGAL Trial of GPS: On December 29, 2025, the Company provided an update on the pivotal Phase 3 REGAL trial, announcing that a total of 72 events had been recorded as of December 26, 2025, with the study remaining fully blinded. After reaching the required pre-specified 80th event, customary database lock and blinded data review procedures must be completed before statistical analysis, unblinding, and disclosure of topline results. Because the final analysis is event-driven, the timing of studies with overall survival as an endpoint can vary; SELLAS will announce the 80th event when it occurs. Phase 2 SLS009 in r/r AML: On December 7, 2025, the Company announced that clinical data from its ongoing Phase 2 study of SLS009, in combination with azacitidine (AZA) and venetoclax (VEN) for the treatment of patients with r/r AML with myelodysplastic syndrome-related changes (AML-MR) after prior VEN-based treatment were presented at the 67th American Society of Hematology (ASH) Annual Meeting and Exposition in December 2025. SLS009 in combination with AZA/VEN demonstrated clinically meaningful activity in patients with R/R AML-MR, and among the 35 evaluable patients, the overall response rate (CR/Cri/MLFS) was 46%, including 29% achieving CR/CRi. Patients harboring ASXL1 or TP53 mutations achieved response rates of 48% and 57%, respectively. The median overall survival (mOS) was exceedingly higher than the expected 2.6 months in this R/R AML patient population, and in the least pretreated cohort, mOS reached 8.9 months. Across all cohorts, patients with one prior line of therapy experienced the greatest benefit, with a 58% response rate and mOS not yet reached. No dose-limiting toxicities (DLTs) or treatment-related deaths were observed, and the combination was well tolerated. Expansion of SLS009 into Earlier-Line AML Treatment: Following the encouraging Phase 2 results of SLS009 in r/r AML particularly in patients with high-risk molecular subtypes, the Company has expanded the development program into earlier lines of therapy. After receiving constructive feedback from the FDA, SELLAS dosed the first patient in an 80-patient trial in newly diagnosed AML patients, as well as those who become refractory early to AZA/VEN treatment which we established through our extensive transcriptomics, genomics, and proteomics models. Preclinical Data on SLS009 in AML at the 2026 American Association for Cancer Research (AACR): The data shows that SLS009 induces apoptosis in AML cell lines, including those harboring high-risk ASXL1 and TP53 mutations. Pharmacodynamic changes were observed as early as 8 hours after treatment and became more pronounced over time, with reductions in MCL-1 and survivin, correlating with increased apoptosis. The poster, entitled, “Tambiciclib (SLS009), a CDK9 inhibitor, promotes apoptosis and suppresses MCL-1 levels in AML cell lines” will be presented on April 21, 2026. Preclinical Data on SLS009 in T-PLL Presented at ESMO 2025: In October 2025, preclinical data demonstrating statistically significant survival benefit of SLS009 were presented at the European Society for Medical Oncology (ESMO) Congress in Berlin, Germany. The results showed that SLS009, as a monotherapy and in combination with VEN, significantly prolonged survival compared to VEN alone in an in vivo patient-derived xenograft model of T-cell prolymphocytic leukemia (T-PLL). These findings further support the therapeutic potential of SLS009 to improve outcomes across multiple hematologic malignancies. Virtual R&D Day on Advancing Novel Therapies in AML: On October 29, 2025, SELLAS hosted a virtual R&D Day on “Advancing Novel Therapies in Acute Myeloid Leukemia (AML)” featuring key opinion leaders and Company management. The event provided a detailed review of the Company’s ongoing Phase 3 REGAL trial of GPS and the SLS009 program, underscoring each therapy’s potential to address multiple stages of disease progression along the AML treatment continuum. To access a replay of the R&D Day, please click here. Received $67.2 Million in Gross Proceeds from Warrant Exercises in 2025: In September and October 2025, SELLAS received a total of approximately $54.6 million in gross proceeds from the immediate exercise of existing warrants, including $23.6 million from warrants issued in January 2025 and $31.0 million from warrants issued in March and August 2024. An additional $12.6 million in proceeds was received during 2025 from the exercise of other previously outstanding warrants. Received Additional $42.6 Million in Proceeds from Warrant Exercises in Q1 2026: Subsequent to December 31, 2025, the Company received an additional $42.6 million in proceeds from the exercise of previously outstanding warrants. These additional proceeds bolster the reported $71.8 million cash and cash equivalents as of December 31, 2025, and provide the Company with the strongest financial position in its history. Financial Results for the Full Year 2025: Research and Development Expenses: Research and development expenses for the year ended December 31, 2025, were $16.0 million, compared to $19.1 million for the year ended December 31, 2024. The decrease was primarily due to decreases in clinical trial expenses and clinical and regulatory consulting costs, which were primarily driven by the completion of enrollment in the REGAL study in the first quarter of 2024. General and Administrative Expenses: General and administrative expenses for the year ended December 31, 2025, were $12.3 million, as compared to $12.4 million for the year ended December 31, 2024. The decrease was primarily attributable to a decrease in personnel related expenses. Net Loss: The net loss was $26.9 million for the year ended December 31, 2025, or a basic and diluted loss per share of $0.25, as compared to a net loss of $30.9 million for the year ended December 31, 2024, or a basic and diluted loss per share of $0.50. Cash Position: As of December 31, 2025, cash and cash equivalents totaled approximately $71.8 million. Subsequent to December 31, 2025, the Company received an additional $42.6 million in proceeds from the exercise of previously outstanding warrants. About SELLAS Life Sciences Group, Inc. SELLAS is a late-stage clinical biopharmaceutical company focused on the development of novel therapeutics for a broad range of cancer indications. SELLAS’ lead product candidate, GPS, is licensed from Memorial Sloan Kettering Cancer Center and targets the WT1 protein, which is present in an array of tumor types. GPS has the potential as a monotherapy and combination with other therapies to address a broad spectrum of hematologic malignancies and solid tumor indications. The Company is also developing SLS009 (tambiciclib) - potentially the first and best-in-class differentiated small molecule CDK9 inhibitor with reduced toxicity and increased potency compared to other CDK9 inhibitors. Data suggests that SLS009 demonstrated a high response rate in AML patients with unfavorable prognostic factors including ASXL1 mutation, commonly associated with poor prognosis in various myeloid diseases. For more information on SELLAS, please visit www.sellaslifesciences.com. Forward-Looking Statements This press release contains forward-looking statements. All statements other than statements of historical facts are “forward-looking statements,” including those relating to future events. In some cases, forward-looking statements can be identified by terminology such as “plan,” “expect,” “anticipate,” “may,” “might,” “will,” “should,” “project,” “believe,” “estimate,” “predict,” “potential,” “intend,” or “continue” and other words or terms of similar meaning. These statements include, without limitation, statements related to the GPS clinical development program, including the REGAL study and the timing of future milestones related thereto. These forward-looking statements are based on current plans, objectives, estimates, expectations, and intentions, and inherently involve significant risks and uncertainties. Actual results and the timing of events could differ materially from those anticipated in such forward-looking statements as a result of these risks and uncertainties, which include, without limitation, risks and uncertainties with oncology product development and clinical success thereof, the uncertainty of regulatory approval, and other risks and uncertainties affecting SELLAS and its development programs as set forth under the caption “Risk Factors” in SELLAS’ Annual Report on Form 10-K filed on March 19, 2026 and in its other SEC filings. Other risks and uncertainties of which SELLAS is not currently aware may also affect SELLAS’ forward-looking statements and may cause actual results and the timing of events to differ materially from those anticipated. The forward-looking statements herein are made only as of the date hereof. SELLAS undertakes no obligation to update or supplement any forward-looking statements to reflect actual results, new information, future events, changes in its expectations, or other circumstances that exist after the date as of which the forward-looking statements were made. Investor Contact John Fraunces Managing Director LifeSci Advisors, LLC [email protected] SELLAS LIFE SCIENCES GROUP, INC. CONSOLIDATED STATEMENTS OF OPERATIONS (Amounts in thousands, except share and per share data) SELLAS LIFE SCIENCES GROUP, INC. CONSOLIDATED BALANCE SHEETS (Amounts in thousands, except share and per share data)

– Hosted Virtual R&D Day Highlighting GPS and SLS009 Programs in AML – – Positive Phase 2 Data for SLS009 in R/R AML Accepted for Presentation at ASH 2025; Initiation of Trial Including Newly Diagnosed First-Line AML Patients Expected in Q1 2026 – – $44.3 Million in Cash and Cash Equivalents as of September 30, 2025; Additional $29.1 Million in Proceeds Received in October 2025 through Warrant Exercises – NEW YORK, Nov. 12, 2025 (GLOBE NEWSWIRE) -- SELLAS Life Sciences Group, Inc. (NASDAQ: SLS) (“SELLAS’’ or the “Company”), a late-stage clinical biopharmaceutical company focused on the development of novel therapies for a broad range of cancer indications, today reported financial results for the third quarter ended September 30, 2025, and provided a corporate update. “We remain highly encouraged by the continued, strong execution across our programs and the expanding body of clinical and preclinical data reinforcing the strength of our AML-focused pipeline,” said Angelos Stergiou, MD, ScD h.c., President and Chief Executive Officer of SELLAS. “The Phase 3 REGAL trial of GPS is advancing as planned as highlighted by the key opinion leaders at our recent R&D event. Momentum around SLS009 also continues to build—our positive Phase 2 data were accepted for presentation at the upcoming ASH Annual Meeting, and we recently presented preclinical results at ESMO demonstrating clear survival benefits in T-PLL.” Dr. Stergiou continued, “Our recent R&D Day was a resounding success and provided an excellent opportunity to share program updates and hear directly from leading experts who expressed genuine enthusiasm for both GPS and SLS009. These achievements highlight the breadth and promise of our pipeline and underscore the complementary potential of our two programs to meaningfully improve outcomes for patients with AML and other hematologic cancers. With a strong financial foundation following the recent warrant exercises and multiple catalysts ahead, we believe SELLAS is entering a transformative period of growth and value creation.” Recent Corporate Highlights: Phase 3 REGAL Trial of GPS: Following the positive IDMC recommendation announced in August to continue the trial without modification, the Phase 3 REGAL trial of GPS in patients with acute myeloid leukemia (AML) who have achieved complete remission following second-line salvage therapy (CR2) remains on track and continues to execute as planned. The final analysis will be conducted once 80 events (deaths) are reached and is anticipated by year-end 2025. Because the final analysis is event driven, it is difficult to predict with any certainty and it may occur at a different time than currently expected. Phase 2 SLS009 (Selective CDK9 Inhibitor) in R/R AML: Following the positive results from the Phase 2 study of SLS009 announced in July, data from the ongoing trial evaluating SLS009 in combination with azacitidine (AZA) and venetoclax (VEN) for the treatment of relapsed or refractory (r/r) AML have been accepted for presentation at the upcoming 67th American Society of Hematology (ASH) Annual Meeting and Exposition, taking place December 6–9, 2025, in Orlando, Florida. The Company continues to advance plans for an 80-patient trial in newly diagnosed AML patients as well as those who become refractory early to AZA/VEN treatment, with enrollment expected to begin in the first quarter of 2026. Preclinical Data on SLS009 in T-PLL Presented at ESMO 2025: In October 2025, preclinical data demonstrating statistically significant survival benefit of SLS009 were presented at the European Society for Medical Oncology (ESMO) Congress in Berlin, Germany. The results showed that SLS009, as a monotherapy and in combination with VEN, significantly prolonged survival compared to VEN alone in an in vivo patient-derived xenograft model of T-cell prolymphocytic leukemia (T-PLL). These findings further support the therapeutic potential of SLS009 to improve outcomes across multiple hematologic malignancies. Virtual R&D Day on Advancing Novel Therapies in AML: On October 29, 2025, SELLAS hosted a virtual R&D Day on “Advancing Novel Therapies in Acute Myeloid Leukemia (AML)” featuring key opinion leaders and Company management. The event provided a detailed review of the Company’s ongoing Phase 3 REGAL trial of GPS and the SLS009 program, underscoring each therapy’s potential to address multiple stages of disease progression along the AML treatment continuum. To access a replay of the R&D Day, please click here. Received $54.6 Million in Gross Proceeds from Warrant Exercises: In September and October 2025, SELLAS received a total of approximately $54.6 million in gross proceeds from the immediate exercise of existing warrants, including $23.6 million from warrants issued in January 2025 and $31.0 million from warrants issued in March and August 2024. Financial Results for the Third Quarter 2025: R&D Expenses: Research and development expenses for the quarter ended September 30, 2025 were $4.2 million compared to $4.4 million for the same period in 2024. The decrease was primarily due to decreases in clinical trial expenses and clinical and regulatory consulting costs. Research and development expenses were $11.3 million for the nine months ended September 30, 2025 compared to $14.7 million for the same period in 2024. The decrease was primarily due to decreases in clinical trial expenses, manufacturing costs and clinical drug supply purchases, and clinical and regulatory consulting costs, which were primarily driven by the completion of enrollment in the REGAL study in the first quarter of 2024. G&A Expenses: General and administrative expenses for the third quarter of 2025 were $2.9 million compared to $3.0 million for the same period in 2024. The decrease was primarily attributable to a decrease in professional fees partially offset by an increase in personnel related expenses, including non-cash stock-based compensation. General and administrative expenses were $8.7 million for the nine months ended September 30, 2025 compared to $9.9 million for the same period in 2024. The decrease was primarily attributable to a decrease in personnel related expenses driven by the initial recognition of a one-time severance charge in the prior period. Net Loss: The net loss was $6.8 million for the third quarter of 2025, or a basic and diluted loss per share of $0.06, as compared to a net loss of $7.1 million for the third quarter of 2024, or a basic and diluted loss per share of $0.10. The net loss was $19.2 million for the nine months ended September 30, 2025, or a basic and diluted net loss per share of $0.20, as compared to a net loss of $24.1 million for the same period in 2024, or a basic and diluted net loss per share of $0.42. Cash Position: As of September 30, 2025, cash and cash equivalents totaled approximately $44.3 million. Subsequent to September 30, 2025, the Company received $29.1 million in net proceeds in October 2025 from warrant exercises. About SELLAS Life Sciences Group, Inc. SELLAS is a late-stage clinical biopharmaceutical company focused on the development of novel therapeutics for a broad range of cancer indications. SELLAS’ lead product candidate, GPS, is licensed from Memorial Sloan Kettering Cancer Center and targets the WT1 protein, which is present in an array of tumor types. GPS has the potential as a monotherapy and combination with other therapies to address a broad spectrum of hematologic malignancies and solid tumor indications. The Company is also developing SLS009 (tambiciclib) - potentially the first and best-in-class differentiated small molecule CDK9 inhibitor with reduced toxicity and increased potency compared to other CDK9 inhibitors. Data suggests that SLS009 demonstrated a high response rate in AML patients with unfavorable prognostic factors including ASXL1 mutation, commonly associated with poor prognosis in various myeloid diseases. For more information on SELLAS, please visit www.sellaslifesciences.com. Forward-Looking Statements This press release contains forward-looking statements. All statements other than statements of historical facts are “forward-looking statements,” including those relating to future events. In some cases, forward-looking statements can be identified by terminology such as “plan,” “expect,” “anticipate,” “may,” “might,” “will,” “should,” “project,” “believe,” “estimate,” “predict,” “potential,” “intend,” or “continue” and other words or terms of similar meaning. These statements include, without limitation, statements related to the GPS clinical development program, including the REGAL study and the timing of future milestones related thereto. These forward-looking statements are based on current plans, objectives, estimates, expectations, and intentions, and inherently involve significant risks and uncertainties. Actual results and the timing of events could differ materially from those anticipated in such forward-looking statements as a result of these risks and uncertainties, which include, without limitation, risks and uncertainties with oncology product development and clinical success thereof, the uncertainty of regulatory approval, and other risks and uncertainties affecting SELLAS and its development programs as set forth under the caption “Risk Factors” in SELLAS’ Annual Report on Form 10-K filed on March 20, 2025 and in its other SEC filings. Other risks and uncertainties of which SELLAS is not currently aware may also affect SELLAS’ forward-looking statements and may cause actual results and the timing of events to differ materially from those anticipated. The forward-looking statements herein are made only as of the date hereof. SELLAS undertakes no obligation to update or supplement any forward-looking statements to reflect actual results, new information, future events, changes in its expectations, or other circumstances that exist after the date as of which the forward-looking statements were made. Investor Contact John Fraunces Managing Director LifeSci Advisors, LLC [email protected]

- Positive IDMC Recommendation to Continue Pivotal Phase 3 REGAL Trial of Galinpepimut-S (GPS) in AML Without Modification; Final Analysis Anticipated by Year-end 2025 – - Reported Positive Phase 2 Results of SLS009 in Relapsed/Refractory (r/r) Acute Myeloid Leukemia (AML) with Trial Meeting All Primary Endpoints; Full Data Presentation Expected Later This Year - - Alignment with FDA to Advance SLS009 in a First-Line AML Trial with Enrollment Anticipated by Q1 2026 - - $25.3 million in Cash and Cash Equivalents as of June 30, 2025; Additional $4.0 million Proceeds Received in July 2025 for Warrant Exercises - NEW YORK, Aug. 12, 2025 (GLOBE NEWSWIRE) -- SELLAS Life Sciences Group, Inc. (NASDAQ: SLS) (“SELLAS’’ or the “Company”), a late-stage clinical biopharmaceutical company focused on the development of novel therapies for a broad range of cancer indications, today reported financial results for the second quarter ended June 30, 2025, and provided a corporate update. “We continue to make significant progress in advancing our AML-focused pipeline, as demonstrated by the positive Phase 2 results evaluating our novel CDK9 inhibitor, SLS009, for the treatment of r/r AML,” said Angelos Stergiou, MD, ScD h.c., President and Chief Executive Officer of SELLAS. “The Phase 2 trial met all primary endpoints, achieving a 44% response rate among patients with Acute Myeloid Leukemia-Myelodysplasia-Related Changes (AML-MRC), which at the optimal dose level, nearly tripled the median overall survival compared to a historical benchmark. Based on the strength of these data, we conducted an end-of-Phase 2 meeting and the FDA recommended advancing SLS009 into the front-line setting for AML. We are now preparing an 80-patient trial that is focused on newly diagnosed and early refractory to venetoclax and azacitidine AML patients, with enrollment anticipated to begin by Q1 2026.” Dr. Stergiou continued, “During the quarter, we also presented promising preclinical data at ASCO supporting SLS009 as a potential targeted therapy for ASXL1 mutated colorectal cancer and strengthened our scientific leadership with the addition of three world-class oncology experts to our Scientific Advisory Board. With the final pivotal Phase 3 REGAL data of GPS in AML expected by year-end, positive Phase 2 data of SLS009 in r/r AML, and our upcoming ESMO presentation showcasing SLS009’s impact in T-PLL, we enter the second half of 2025 with tremendous momentum and a clear focus on advancing our late-stage clinical programs and growing shareholder value.” Recent Corporate Highlights: Phase 3 REGAL Trial of GPS: On August 7, 2025, SELLAS announced that the IDMC completed a pre-specified analysis of the Phase 3 REGAL trial of GPS in AML and issued a positive recommendation to continue the trial without modification. The IDMC concluded that the risk-benefit profile of GPS supports continued evaluation under the current study protocol. No safety concerns were identified, and available efficacy data were consistent with expectations for continued trial conduct. The final analysis will be conducted once 80 events (deaths) are reached and is anticipated by year-end. Announced Positive Results from Phase 2 Trial of SLS009 in r/r AML: The trial met all primary endpoints, demonstrating a 44% response rate among patients with Acute Myeloid Leukemia-Myelodysplasia-Related Changes (AML-MRC) at an optimal dose of 30 mg twice weekly and 50% in AML-MRC with myelomonocytic/myelomonoblastic (M4/M5) subtype, significantly exceeding the targeted 20% ORR. In addition, the treatment achieved a median overall survival (mOS) of 8.9 months in AML-MRC patients, while all relapsed or refractory to venetoclax-based regimens patients receiving 30 mg BIW achieved a mOS of 8.8 months, far surpassing the historical benchmark of 2.4 months. SLS009 End-of-Phase 2 Meeting: The FDA recommended that SELLAS proceed into a trial to include newly diagnosed, first-line AML patients eligible for venetoclax/azacitidine (aza/ven) therapy, where the Agency believes clinical benefit might be greatest. The randomized 80-patient trial is currently in preparation and is expected to begin enrollment by Q1 2026. The FDA indicated a preference for response rate as the primary endpoint. The trial will include two groups: 1) predictive biomarker cohort of newly diagnosed patients unlikely to benefit from standard aza/ven therapy based on molecular profiling, and 2) early resistance cohort of patients who initiate treatment with aza/ven but demonstrate confirmed lack of any response after two treatment cycles. Whether additional patients will be needed – either for broader study expansion or only within one of the study arms – will depend on the outcomes observed in the initial cohorts (n=40 per arm). This study may support a New Drug Application (NDA), including accelerated approval. Presented Preclinical Efficacy of SLS009 in ASXL1 Mutated Colorectal Cancer at ASCO 2025: The presentation demonstrated SLS009’s ability to selectively target ASXL1-driven tumors at concentrations well below the known safety threshold. The ASXL1 mutation status could serve as a potential biomarker for response to SLS009 inhibition, which may allow the Company to further refine patient selection and improve outcomes. Expanded Scientific Advisory Board: New members, Philip C. Amrein, MD, Alex Kentsis, MD, PhD, and Linghua Wang, MD, PhD, bring decades of expertise in cancer research, clinical oncology, and translational medicine, further strengthening the Company’s strategic guidance as it advances its pipeline. Announced Inclusion in the Russell 3000® and Russell 2000® Indexes: The Russell 3000® Index tracks the performance of the largest 3,000 publicly traded U.S. companies and serves as a broad benchmark for the U.S. equity market. The Russell 2000® Index, a subset of the Russell 3000®, measures the performance of the small-cap stocks and represents approximately 10% of the total market capitalization of the U.S. equity market. Preclinical Efficacy of SLS009 in T-Cell Prolymphocytic Leukemia (T-PLL) to be Showcased at ESMO 2025: The poster, entitled, CDK9 Inhibition Enhances Venetoclax Activity and Prolongs Survival in a T-PLL Patient-Derived Xenograft Model, will be presented during the ESMO congress to be held in Berlin, 17-21 October 2025. Financial Results for the Second Quarter 2025: R&D Expenses: Research and development expenses for the quarter ended June 30, 2025 were $3.9 million compared to $5.2 million for the same period in 2024. Research and development expenses in the first half of 2025 were $7.1 million compared to $10.3 million for the same period in 2024. The decrease was primarily due to decreases in clinical trial expenses, manufacturing costs and clinical drug supply purchases, and clinical and regulatory consulting costs, which were primarily driven by the completion of enrollment in the REGAL study in the first quarter of 2024. G&A Expenses: General and administrative expenses for the second quarter of 2025 were $3.0 million compared to $2.4 million for the same period in 2024. The $0.6 million increase was primarily attributable to increases in professional fees, personnel related expenses, including non-cash stock-based compensation, and outside services and public company costs. General and administrative expenses were $5.9 million for the first half of 2025 compared to $7.0 million for the same period in 2024. The $1.1 million decrease was primarily attributable to a decrease in personnel related expenses driven by the initial recognition of a one-time severance charge in the prior period. Net Loss: The net loss was $6.6 million for the second quarter of 2025, or a basic and diluted loss per share of $0.07, compared to a net loss of $7.5 million for the second quarter of 2024, or a basic and diluted loss per share of $0.13. The net loss was $12.4 million for the first half of 2025, or a basic and diluted net loss per share of $0.13, compared to a net loss of $17.0 million for the first half of 2024, or a basic and diluted net loss per share of $0.33. Cash Position: As of June 30, 2025, cash and cash equivalents totaled approximately $25.3 million. Subsequent to June 30, 2025, the Company received $4.0 million in proceeds in July 2025 from the exercise of warrants. About SELLAS Life Sciences Group, Inc. SELLAS is a late-stage clinical biopharmaceutical company focused on the development of novel therapeutics for a broad range of cancer indications. SELLAS’ lead product candidate, GPS, is licensed from Memorial Sloan Kettering Cancer Center and targets the WT1 protein, which is present in an array of tumor types. GPS has the potential as a monotherapy and combination with other therapies to address a broad spectrum of hematologic malignancies and solid tumor indications. The Company is also developing SLS009 (tambiciclib) - potentially the first and best-in-class differentiated small molecule CDK9 inhibitor with reduced toxicity and increased potency compared to other CDK9 inhibitors. Data suggests that SLS009 demonstrated a high response rate in AML patients with unfavorable prognostic factors including ASXL1 mutation, commonly associated with poor prognosis in various myeloid diseases. For more information on SELLAS, please visit www.sellaslifesciences.com Forward-Looking Statements This press release contains forward-looking statements. All statements other than statements of historical facts are “forward-looking statements,” including those relating to future events. In some cases, forward-looking statements can be identified by terminology such as “plan,” “expect,” “anticipate,” “may,” “might,” “will,” “should,” “project,” “believe,” “estimate,” “predict,” “potential,” “intend,” or “continue” and other words or terms of similar meaning. These statements include, without limitation, statements related to the GPS clinical development program, including the REGAL study and the timing of future milestones related thereto. These forward-looking statements are based on current plans, objectives, estimates, expectations, and intentions, and inherently involve significant risks and uncertainties. Actual results and the timing of events could differ materially from those anticipated in such forward-looking statements as a result of these risks and uncertainties, which include, without limitation, risks and uncertainties with oncology product development and clinical success thereof, the uncertainty of regulatory approval, and other risks and uncertainties affecting SELLAS and its development programs as set forth under the caption “Risk Factors” in SELLAS’ Annual Report on Form 10-K filed on March 20, 2025 and in its other SEC filings. Other risks and uncertainties of which SELLAS is not currently aware may also affect SELLAS’ forward-looking statements and may cause actual results and the timing of events to differ materially from those anticipated. The forward-looking statements herein are made only as of the date hereof. SELLAS undertakes no obligation to update or supplement any forward-looking statements to reflect actual results, new information, future events, changes in its expectations, or other circumstances that exist after the date as of which the forward-looking statements were made. Investor Contact John Fraunces Managing Director LifeSci Advisors, LLC [email protected]

– Announced Positive Overall Survival in Cohort 3 from the Ongoing Phase 2 Trial of SLS009 (tambiciclib) in Relapsed/Refractory (r/r) Acute Myeloid Leukemia (AML) Demonstrating 8.9 mOS in AML-MRC and 8.8 mOS in All r/r to Venetoclax-Based Regimens Patients – – SLS009 Shows Promising Efficacy in Pediatric Acute Lymphoblastic Leukemia (ALL) Xenograft Models – – Final Analysis of Pivotal Phase 3 REGAL Trial of Galinpepimut-S (GPS) in AML Anticipated in 2025 – – $28.4 million in Cash and Cash Equivalents as of March 31, 2025; Additional $4.0 million Proceeds received in April 2025 through Warrant Exercises – NEW YORK, May 13, 2025 (GLOBE NEWSWIRE) -- SELLAS Life Sciences Group, Inc. (NASDAQ: SLS) (“SELLAS” or the “Company”), a late-stage clinical biopharmaceutical company focused on the development of novel therapies for a broad range of cancer indications, today reported financial results for the first quarter ended March 31, 2025, and provided a corporate update. “We are very encouraged by the strong momentum across our pipeline,” said Angelos Stergiou, MD, ScD h.c., President and Chief Executive Officer of SELLAS. “The positive overall survival data in cohort 3 from the ongoing Phase 2 trial of SLS009 in r/r AML, showing a median OS that exceeds all historical benchmarks by over 3 times, further underscores the transformative potential of SLS009 for many underserved patients. In parallel, our new preclinical findings demonstrating the ability of SLS009 to overcome TP53-driven resistance, along with the promising clinical efficacy from the ongoing Phase 2, give us renewed optimism for patients across different genetic AML mutations. We look forward to presenting further data on SLS009 at ASCO, highlighting its preclinical efficacy in ASXL1-mutated colorectal cancer lines. With the full topline Phase 2 data of SLS009 anticipated soon, and the final analysis of our Phase 3 pivotal REGAL trial of GPS in AML expected later this year, we are well-positioned for an exciting and meaningful 2025.” Recent Corporate Highlights: Announced Positive Overall Survival in Cohort 3 from the Ongoing Phase 2 Trial of SLS009 in r/r AML: The data demonstrated that patients with AML-Myelodysplasia-Related Changes (AML-MRC) achieved a mOS of 8.9 months, while all relapsed or refractory to venetoclax-based regimens patients receiving 30 mg BIW achieved a mOS of 8.8 months, far surpassing the historical benchmark of 2.5 months. In addition, the therapy demonstrated a 67% ORR in patients with AML-MRC and 46% in all evaluable patients, significantly exceeding the targeted 20% ORR. The trial continues with full data and FDA regulatory path feedback expected in 1H 2025. Presented Preclinical Data Highlighting Efficacy of SLS009 in TP53 Mutated AML at the 2025 AACR Conference: Preclinical data suggest that SLS009 can induce apoptosis downstream of p53 by targeting critical proteins such as MCL-1 and survivin, regardless of p53 status. Immunoblot analysis reveals near-complete removal of these proteins in treated cells within 8 hours of exposure to SLS009. Furthermore, the treatment reduced TP53-mutated leukemia cell populations by up to 97% in combination with azacitidine–venetoclax, and by up to 80% as monotherapy. Preclinical Efficacy of SLS009 in ASXL1 Mutated Colorectal Cancer to be Showcased at ASCO 2025: The poster, entitled, In vitro efficacy of CDK9 inhibitor tambiciclib (SLS009) in ASXL1 mutated colorectal cancer cell lines, will be presented on Monday, June 2, 2025, 1:30 PM-4:30 PM CDT. Announced Positive Outcome of Interim Analysis for Phase 3 REGAL Trial of GPS in AML: The interim futility, efficacy, and safety analysis was designed to assess whether the therapy is safe, demonstrates potential efficacy, and merits continuation. The IDMC’s review supports the continuation of the study according to its original protocol. Based on this positive evaluation, GPS has shown preliminary signals of effectiveness, allowing the trial to advance toward completion. Fewer than 50% of enrolled patients were confirmed deceased after the median follow-up of 13.5 months, indicating a median survival of over 13.5 months in the trial vs. a historical median survival of 6 months for conventional therapy, as reported in a similar Phase 2 study. The next and final analysis will be conducted once 80 events (deaths) are reached, further determining the potential of GPS in addressing the needs of AML patients. SELLAS anticipates that 80 events will be reached this year. Announced Promising Data from Phase 2a Trial of SLS009 in Combination with Zanubrutinib in DLBCL: The trial, conducted and funded by GenFleet Therapeutics (Shanghai), Inc. (“Genfleet”), was an open-label single-arm multicenter Phase 2a study in China evaluating SLS009 in combination with BTK inhibitor, Brukinsa® (zanubrutinib) in r/r DLBCL. The results showed an overall response rate (ORR) of 67%, more than double the expected ORR of zanubrutinib alone. Among responders, one achieved complete response (CR), while three had partial response (PR) with target lesion shrinkages of 89%, 78%, and 56%, respectively. As of the last follow-up, after the median of 4.6 (range: 1.4 - 7.4) months follow-up, median overall survival (OS) was not reached, and 6 out of 9 patients were alive. GenFleet will determine the next steps in development around lymphoma as SELLAS’ focus remains on AML and spliceosome–chromatin mutations, including ASXL1 mutations. PIVOT - Received Preliminary Data for Pediatric Acute Lymphoblastic Leukemia (ALL) Patients Derived Xenografts (PDX): The experiment conducted and funded by the National Institute of Health (NIH) through the PIVOT program included 27 patient-derived ALL tumors from pediatric patients. Tumors were xenografted in mice in two groups: vehicle control arm and SLS009 arm. Mice were treated with a fractionated dose once per week for 6 consecutive weeks. The treatment was well tolerated. For all models, median survival was approximately tripled in the SLS009 arm compared to the vehicle control arm. SLS009 demonstrated delayed progression in 25/27 (93%) models and more than 2 times longer time to progression in 15/27 (56%) of ALL models. In addition, there were complete responses (CR) in 2 models, and in one of the two models, CR was maintained after the treatment had been completed until the end of the study (4 months). Among 7 KMT2A rearranged models, time to progression was extended in all 7 models, and in 6/7 (86%) time to progression was more than doubled. Raised $25.0 Million of Gross Proceeds from a Registered Direct Offering Priced At-the-Market under Nasdaq Rules: On January 28, 2025, SELLAS announced the closing of a $25 million registered direct offering with a single healthcare-focused institutional investor before deducting placement agent’s fees and related offering expenses. The net proceeds from the offering strengthens the Company’s financial position and will be used for working capital purposes and general corporate procedures, including the purchase of any pending or future acquisitions. Financial Results for the First Quarter 2025: R&D Expenses: Research and development expenses for the quarter ended March 31, 2025, were $3.2 million, compared to $5.1 million for the same period in 2024. The $1.9 million decrease was primarily due to decreases in clinical trial expenses, manufacturing costs, and clinical drug supply purchases, and clinical and regulatory consulting costs primarily driven by the completion of enrollment in the REGAL study in the first quarter of 2024. G&A Expenses: General and administrative expenses for the first quarter of 2025 were $2.9 million, as compared to $4.5 million for the same period in 2024. The $1.6 million decrease was primarily attributable to a decrease in personnel related expenses driven by the initial recognition of a one-time severance charge during the three months ended March 31, 2024, and a decrease in headcount, and decreases in professional fees and other general and administrative expenses. Net Loss: The net loss was $5.8 million for the first quarter of 2025, or a basic and diluted loss per share of $0.07, as compared to a net loss of $9.6 million for the first quarter of 2024, or a basic and diluted loss per share of $0.21. Cash Position: As of March 31, 2025, cash and cash equivalents totaled approximately $28.4 million. Subsequent to March 31, 2025, the Company received $4.0 million in proceeds from the exercise of warrants. About SELLAS Life Sciences Group, Inc. SELLAS is a late-stage clinical biopharmaceutical company focused on the development of novel therapeutics for a broad range of cancer indications. SELLAS’ lead product candidate, GPS, is licensed from Memorial Sloan Kettering Cancer Center and targets the WT1 protein, which is present in an array of tumor types. GPS has the potential as a monotherapy and combination with other therapies to address a broad spectrum of hematologic malignancies and solid tumor indications. The Company is also developing SLS009 (tambiciclib) - potentially the first and best-in-class differentiated small molecule CDK9 inhibitor with reduced toxicity and increased potency compared to other CDK9 inhibitors. Data suggests that SLS009 demonstrated a high response rate in AML patients with unfavorable prognostic factors including ASXL1 mutation, commonly associated with poor prognosis in various myeloid diseases. For more information on SELLAS, please visit www.sellaslifesciences.com. Forward-Looking Statements This press release contains forward-looking statements. All statements other than statements of historical facts are “forward-looking statements,” including those relating to future events. In some cases, forward-looking statements can be identified by terminology such as “plan,” “expect,” “anticipate,” “may,” “might,” “will,” “should,” “project,” “believe,” “estimate,” “predict,” “potential,” “intend,” or “continue” and other words or terms of similar meaning. These statements include, without limitation, statements related to the GPS clinical development program, including the REGAL study and the timing of future milestones related thereto. These forward-looking statements are based on current plans, objectives, estimates, expectations, and intentions, and inherently involve significant risks and uncertainties. Actual results and the timing of events could differ materially from those anticipated in such forward-looking statements as a result of these risks and uncertainties, which include, without limitation, risks and uncertainties with oncology product development and clinical success thereof, the uncertainty of regulatory approval, and other risks and uncertainties affecting SELLAS and its development programs as set forth under the caption “Risk Factors” in SELLAS’ Annual Report on Form 10-K filed on March 20, 2025 and in its other SEC filings. Other risks and uncertainties of which SELLAS is not currently aware may also affect SELLAS’ forward-looking statements and may cause actual results and the timing of events to differ materially from those anticipated. The forward-looking statements herein are made only as of the date hereof. SELLAS undertakes no obligation to update or supplement any forward-looking statements to reflect actual results, new information, future events, changes in its expectations, or other circumstances that exist after the date as of which the forward-looking statements were made. Investor Contact Bruce Mackle Managing Director LifeSci Advisors, LLC [email protected]

– Announced Positive Outcome of Interim Analysis for its Pivotal Phase 3 REGAL Trial of Galinpepimut-S (GPS) in Acute Myeloid Leukemia (AML) with Next and Final Analysis Planned Upon Reaching 80 Events, Anticipated in 2025 – – Reported Positive Overall Survival and Overall Response Rate Data from the Ongoing Phase 2 Trial of SLS009 (Tambiciclib) in r/r AML – Full Data and FDA Regulatory Path Feedback Expected in 1H 2025 – – Raised $25 Million in Gross Proceeds in a Registered Direct Offering in January 2025 – NEW YORK, March 20, 2025 (GLOBE NEWSWIRE) -- SELLAS Life Sciences Group, Inc. (NASDAQ: SLS) (“SELLAS’’ or the “Company”), a late-stage clinical biopharmaceutical company focused on the development of novel therapies for a broad range of cancer indications, today reported financial results for the full year ended December 31, 2024, and provided a corporate update. “We are pleased with the progress of our pipeline as we continue to advance our two key assets through clinical development,” said Angelos Stergiou, MD, ScD h.c., President and Chief Executive Officer of SELLAS. “The most anticipated milestones in 2025 will be the final analysis of our Phase 3 pivotal REGAL trial of GPS in acute myeloid leukemia (AML) and the full topline Phase 2 data of SLS009 in AML, both of which represent significant opportunities and offer hope to AML patients in need. If successful, the REGAL trial provides a pathway for regulatory approval in AML, and GPS could become a transformative treatment for patients in their second complete remission. Furthermore, the promising data from the ongoing Phase 2 trial of SLS009 has shown a 56% overall response rate (ORR) in AML patients with myelodysplasia-related changes (AML MRC) prospectively enrolled in two expansion cohorts, exceeding the prespecified target ORR of 33%. In the optimal dosing regimen of 30 mg BIW, the median overall survival (mOS) has not been reached but exceeds 7.7 months at the latest follow-up, where the expected mOS is historically approximately 2.5 months.” Dr. Stergiou continued, “We are especially encouraged by the multiple regulatory designations granted to our programs in 2024, including three FDA Rare Pediatric Disease Designations, one FDA Fast Track Designation, and two EMA Orphan Drug Designations, which reflect the significant potential impact of our therapies and provide valuable regulatory benefits that may accelerate development and potential approval. With strong regulatory recognition and two potentially pivotal inflection points ahead, we remain committed to driving innovation and delivering value to patients and shareholders.” Recent Highlights: Announced Positive Outcome of Interim Analysis for Phase 3 REGAL Trial of GPS in AML: The interim futility, efficacy, and safety analysis was designed to assess whether the therapy is safe, demonstrates potential efficacy, and merits continuation. The IDMC’s review supports the continuation of the study according to its original protocol. Based on this positive evaluation, GPS has shown preliminary signals of effectiveness, allowing the trial to advance toward completion. Fewer than 50% of enrolled patients were confirmed deceased after the median follow-up of 13.5 months, indicating a median survival of over 13.5 months in the trial vs. historical median survival of 6 months for conventional therapy, as reported in a similar Phase 2 study. The next and final analysis will be conducted once 80 events (deaths) are reached, further determining the potential of GPS in addressing the needs of AML patients. SELLAS anticipates that 80 events will be reached this year. Promising Data from Phase 2a Trial of SLS009 in Combination with Zanubrutinib in DLBCL: The trial, conducted and funded by GenFleet Therapeutics (Shanghai), Inc. (“Genfleet”), was an open-label single-arm multicenter Phase 2a study in China evaluating SLS009 in combination with BTK inhibitor, Brukinsa® (zanubrutinib) in r/r DLBCL. The results showed an overall response rate (ORR) of 67%, more than double the expected ORR of zanubrutinib alone. Among responders, one achieved complete response (CR), while three had partial response (PR) with target lesion shrinkages of 89%, 78%, and 56%, respectively. As of the last follow-up, after the median of 4.6 (range: 1.4 - 7.4) months follow-up, median overall survival (OS) was not reached, and 6 out of 9 patients were alive. GenFleet will determine the next steps in development around lymphoma as SELLAS’ focus remains on AML and spliceosome–chromatin mutations, including ASXL1 mutations. Raised $25.0 Million of Gross Proceeds from a Registered Direct Offering Priced At-the-Market under Nasdaq Rules: On January 28, 2025, SELLAS announced the closing of a $25 million registered direct offering with a single healthcare-focused institutional investor before deducting placement agent’s fees and related offering expenses. The net proceeds from the offering strengthens the Company’s financial position and will be used for working capital purposes and general corporate procedures, including the purchase of any pending or future acquisitions. 2024 Key Achievements: SLS009 (tambiciclib): highly selective CDK9 inhibitor The World Health Organization (WHO) approved “tambiciclib” as the recommended International Nonproprietary Name (INN) for SLS009. Reported positive data from the ongoing Phase 2 trial of SLS009 in r/r AML in Q4 2024. The median overall survival (mOS) has not been reached but exceeds 7.7 months at the latest follow-up, where the expected mOS is historically ~ 2.5 months. In expansion cohorts in patients with AML-myelodysplasia-related changes (AML-MRC) with ASXL1 mutation and mutations and cytogenic changes other than ASXL1, the ORR was 56% in 9 patients evaluable for efficacy, exceeding pre-specified target response rate of 33%. Presented data from Phase 2a trial of SLS009 in r/r AML at the 66th American Society of Hematology (ASH) Annual Meeting & Exposition 2024. Completed enrollment in Phase 2a Trial of SLS009 in r/r AML: 30 patients relapsed after or refractory to venetoclax-based regiments were enrolled ahead of schedule in 5 centers across the US. Opened enrollment in additional Phase 2 cohorts in venetoclax combinations in r/r AML. Development of SLS009 continues with the opening of two new cohorts - AML MRC with ASXL1 mutations and AML with myelodysplasia-related changes other than ASXL1 mutations. These new cohorts are also open for enrollment of certain pediatric patients. Announced positive preclinical data indicating ASXL1 mutations as predictors of response to SLS009 in solid cancers. Published in Oncotarget, revealing the underlying mechanisms of action behind the anti-proliferative effects of SLS009 in various hematologic malignancies. Continued National Cancer Institute (NCI) Pediatric Preclinical in Vivo Testing (PIVOT) Program in pediatric tumors. Regulatory: Received multiple regulatory designations: for GPS, FDA Rare Pediatric Disease Designation (RPDD) for pediatric AML; and for SLS009, RPDD for pediatric AML, pediatric acute lymphoblastic leukemia (ALL), FDA Fast Track Designation for AML, and EMA orphan drug designation (ODD) for AML and peripheral T-cell lymphoma (PTCL). Financial Results for the Full Year 2024: R&D Expenses: Research and development expenses for the year ended December 31, 2024, were $19.1 million, compared to $24.0 million for the year ended December 31, 2023. The decrease was primarily due to decreases in clinical trial expenses, manufacturing costs and clinical drug supply purchases, and clinical and regulatory consulting costs primarily driven by the completion of enrollment in the REGAL study in the first quarter of 2024 and a decrease in employee-related expenses due to a decrease in headcount. G&A Expenses: General and administrative expenses for the year ended December 31, 2024, were $12.4 million, as compared to $13.9 million for the year ended December 31, 2023. The decrease was primarily due to a decrease in employee-related expenses due to a decrease in headcount, outside services and public company costs, and insurance premiums, partially offset by a one-time severance charge in 2024 and an increase in legal fees. Net Loss: The net loss was $30.9 million for the year ended December 31, 2024, or a basic and diluted loss per share of $0.50, as compared to a net loss of $37.3 million for the year ended December 31, 2023, or a basic and diluted loss per share of $1.34. Cash Position: As of December 31, 2024, cash and cash equivalents totaled approximately $13.9 million. Subsequent to December 31, 2024, on January 28, 2025, the Company received gross proceeds of $25.0 million from a registered direct offering priced at-the-market under Nasdaq rules. About SELLAS Life Sciences Group, Inc. SELLAS is a late-stage clinical biopharmaceutical company focused on the development of novel therapeutics for a broad range of cancer indications. SELLAS’ lead product candidate, GPS, is licensed from Memorial Sloan Kettering Cancer Center and targets the WT1 protein, which is present in an array of tumor types. GPS has the potential as a monotherapy and combination with other therapies to address a broad spectrum of hematologic malignancies and solid tumor indications. The Company is also developing SLS009 (tambiciclib) - potentially the first and best-in-class differentiated small molecule CDK9 inhibitor with reduced toxicity and increased potency compared to other CDK9 inhibitors. Data suggests that SLS009 demonstrated a high response rate in AML patients with unfavorable prognostic factors including ASXL1 mutation, commonly associated with poor prognosis in various myeloid diseases. For more information on SELLAS, please visit www.sellaslifesciences.com. Forward-Looking Statements This press release contains forward-looking statements. All statements other than statements of historical facts are “forward-looking statements,” including those relating to future events. In some cases, forward-looking statements can be identified by terminology such as “plan,” “expect,” “anticipate,” “may,” “might,” “will,” “should,” “project,” “believe,” “estimate,” “predict,” “potential,” “intend,” or “continue” and other words or terms of similar meaning. These statements include, without limitation, statements related to the GPS clinical development program, including the REGAL study and the timing of future milestones related thereto. These forward-looking statements are based on current plans, objectives, estimates, expectations, and intentions, and inherently involve significant risks and uncertainties. Actual results and the timing of events could differ materially from those anticipated in such forward-looking statements as a result of these risks and uncertainties, which include, without limitation, risks and uncertainties with oncology product development and clinical success thereof, the uncertainty of regulatory approval, and other risks and uncertainties affecting SELLAS and its development programs as set forth under the caption “Risk Factors” in SELLAS’ Annual Report on Form 10-K filed on March 20, 2025 and in its other SEC filings. Other risks and uncertainties of which SELLAS is not currently aware may also affect SELLAS’ forward-looking statements and may cause actual results and the timing of events to differ materially from those anticipated. The forward-looking statements herein are made only as of the date hereof. SELLAS undertakes no obligation to update or supplement any forward-looking statements to reflect actual results, new information, future events, changes in its expectations, or other circumstances that exist after the date as of which the forward-looking statements were made. Investor Contact Bruce Mackle Managing Director LifeSci Advisors, LLC [email protected]