BOLD

Enrollment proceeding in KOMODO-1 first-in-human clinical trial of BBI-940 $93 million in cash provides runway through expected clinical proof-of-concept readout for KOMODO-1 SAN DIEGO, May 08, 2026 (GLOBE NEWSWIRE) -- Boundless Bio (Nasdaq: BOLD), a clinical-stage oncology company interrogating extrachromosomal DNA (ecDNA) biology to deliver transformative therapies to patients with previously intractable oncogene amplified cancers, today announced financial results and business highlights for the fiscal quarter ended March 31, 2026. “We are encouraged by the progress of the KOMODO-1 trial," said Zachary Hornby, President and Chief Executive Officer of Boundless Bio. “We continue to expand the body of evidence supporting BBI-940’s kinesin degradation mechanism, with our recent AACR poster demonstrating anti-tumor activity and tumor regression across multiple ecDNA+ cancer models. These findings further strengthen our confidence in the therapeutic potential of BBI-940 as we advance the program through a first-in-human clinical trial.” Business Highlights and Upcoming Milestones BBI-940 Novel Kinesin Degrader Clinical Program Enrollment is ongoing in KOMODO-1 (Kinesin Oral Molecular Degrader for Oncology-1), a first-in-human clinical trial of BBI-940 in patients with estrogen receptor positive and human epidermal growth factor receptor 2 negative (ER+/HER2-) breast cancer who have progressed following treatment with a cyclin-dependent kinase 4 and/or 6 (CDK4/6) inhibitor plus endocrine therapy, as well as patients with triple-negative breast cancer luminal androgen receptor subtype (TNBC-LAR). Initial safety and efficacy clinical proof-of-concept data are expected within the Company’s existing cash runway timeline. Validating Kinesin Degradation Data Presented at 2026 AACR Annual Meeting In vitro and in vivo study data were presented at the American Association for Cancer Research (AACR) Annual Meeting 2026, which demonstrated that genetic depletion and pharmacologic degradation of a novel kinesin (Kinesin) cause ecDNA mis-segregation, ecDNA reduction, and reduced viability of ecDNA positive (ecDNA+) cancer cells. Further, selective degradation of Kinesin in a panel of tumor cell lines demonstrated sensitivity across multiple tumor types, including 32% of breast cancer cell lines, including those positive for ecDNA and FGFR1 gain. This molecularly defined subgroup for Kinesin degradation sensitivity was further validated in vivo with demonstrated monotherapy tumor regressions in an ecDNA+ TNBC-LAR model, and significant antitumor activity as monotherapy and in combination with fulvestrant in an ecDNA+/FGFR1+ ER+ breast cancer model. First Quarter 2026 Financial Results Cash Position: Cash, cash equivalents, and short-term investments totaled $92.8 million as of March 31, 2026. The Company expects its cash to fund operations into the second half of 2028. Research and Development (R&D) Expenses: R&D expenses were $9.7 million for the first quarter of 2026 compared to $12.1 million for the same period in 2025. General and Administrative (G&A) Expenses: G&A expenses were $4.7 million for the first quarter of 2026 compared to $5.2 million for the same period in 2025. Net Loss: Net loss totaled $13.6 million for the first quarter of 2026 compared to $15.8 million for the same period in 2025. About Boundless Bio Boundless Bio is a clinical-stage oncology company dedicated to unlocking a new paradigm in cancer therapeutics that addresses the significant unmet need in patients with oncogene amplified tumors. Boundless Bio’s research focuses on extrachromosomal DNA (ecDNA), a root cause of oncogene amplification observed in 14% to 17% of cancer patients. Boundless Bio is developing BBI-940, a potentially first-in-class, oral, selective Kinesin degrader as an ecDNA-directed therapeutic candidate (ecDTx). Boundless Bio is headquartered in San Diego, California. For more information, visit https://boundlessbio.com/and follow us on LinkedIn and X. Forward-Looking Statements Boundless Bio, Inc. (the Company) cautions you that statements contained in this press release that are not a description of historical facts are forward-looking statements. In some cases, you can identify forward-looking statements by terms such as “anticipate,” “believe,” “contemplate,” “continue,” “could,” “estimate,” “expect,” “intend,” “may,” “plan,” “potential,” “predict,” “project,” “should,” “would,” “target,” or “will” or the negative of these terms or other similar expressions. Forward-looking statements are based on the Company’s current beliefs and expectations and include but are not limited to statements regarding: plans to continue enrollment in and advance the KOMODO-1 trial through initial clinical proof-of-concept data; the expected timing of an initial clinical proof-of-concept readout from the KOMODO-1 trial; the significance of data from preclinical studies of BBI-940; the Company’s cash runway and the sufficiency thereof to fund operations through the anticipated initial clinical proof-of-concept readout from the KOMODO-1 trial; the potential safety and therapeutic benefits of BBI-940 as a monotherapy and in combination with fulvestrant; and BBI-940’s potential to become a first-in-class drug product. The Company’s actual results and performance may differ materially from those expressed or implied in any forward-looking statement due to substantial known and unknown risks and uncertainties, including, without limitation: potential delays in the enrollment, data readouts, or completion of clinical trials or in regulatory submissions and responses; the Company may use its capital resources sooner than it expects; the Company may be unable to obtain necessary additional funding when needed, on acceptable terms, or at all; the Company is early in its development efforts and its approach to discover and develop ecDTx to treat oncogene amplified cancers is novel and unproven; clinical and preclinical development of therapeutics involves a lengthy and expensive process with inherently uncertain timelines and outcomes; results from preclinical studies or early clinical trials not necessarily being predictive of future results; unexpected adverse side effects or other safety risks or inadequate efficacy of the Company’s ecDTx that may delay or limit their development, regulatory approval, and/or commercialization; the Company’s ability to retain key personnel; the Company’s dependence on third parties in connection with clinical trials, preclinical studies, and manufacturing; the Company may expend its limited resources to pursue a particular ecDTx or combination therapy and fail to capitalize on ecDTx with greater development or commercial potential; the potential for the Company’s programs and prospects to be negatively impacted by developments relating to its competitors, including the results of studies or regulatory determinations relating to its competitors; regulatory and healthcare reform developments in the United States and foreign countries; disruptions or changes at the U.S. Food and Drug Administration (FDA) or other government agencies that limit the FDA’s ability to perform routine activities or function in the normal course or impact the regulatory approval pathway or commercial potential for the Company’s ecDTx; the Company’s ability to obtain, maintain, defend, and enforce patent or other intellectual property protection for its ecDTx and technology; macroeconomic and geopolitical events and conditions, including international trade policies and tariffs, military conflicts, inflation, supply chain disruptions, market volatility, slowed economic growth or recession; and other risks described in the Company’s filings with the Securities and Exchange Commission (SEC), including under the heading “Risk Factors” in the Company’s annual report on Form 10-K for the year ended December 31, 2025 and any subsequent filings with the SEC. You are cautioned not to place undue reliance on forward-looking statements, which speak only as of the date hereof, and, except as required by law, the Company undertakes no obligation to update such statements to reflect events that occur or circumstances that exist after the date hereof. All forward-looking statements are qualified in their entirety by this cautionary statement, which is made under the safe harbor provisions of the Private Securities Litigation Reform Act of 1995. Investor Contacts: James Lee, Boundless Bio [email protected] Jon Nugent, THRUST [email protected] Media Contact: Carly Scaduto, THRUST [email protected]

KOMODO-1 first-in-human clinical trial of BBI-940 open for enrollment $108 million in cash provides runway into the second half of 2028, through expected clinical proof-of-concept readout for KOMODO-1 SAN DIEGO, March 09, 2026 (GLOBE NEWSWIRE) -- Boundless Bio (Nasdaq: BOLD), a clinical-stage oncology company interrogating extrachromosomal DNA (ecDNA) biology to deliver transformative therapies to patients with previously intractable oncogene amplified cancers, today announced financial results and business highlights for the fiscal quarter and full year ended December 31, 2025. "With the KOMODO-1 trial of BBI-940 actively enrolling, we are excited to evaluate this potentially first-in-class oral Kinesin degrader in patients with breast cancer who are seeking new treatment options. BBI-940 is designed to disrupt ecDNA segregation and inheritance, a differentiated mechanism for targeting chromosomally unstable cancers. The Boundless team is focused on clinical execution and reaching an initial proof-of-concept readout within our existing cash runway," said Zachary Hornby, President and Chief Executive Officer of Boundless Bio. Business Highlights and Upcoming Milestones BBI-940 novel Kinesin degrader program In January 2026, the U.S. Food and Drug Administration accepted the Company’s Investigational New Drug application for BBI-940, a novel, selective, oral Kinesin degrader. KOMODO-1 (Kinesin Oral Molecular Degrader for Oncology-1), a first-in-human clinical trial of BBI-940 in patients with estrogen receptor positive and human epidermal growth factor receptor 2 negative (ER+/HER2-) breast cancer who have progressed following treatment with a cyclin-dependent kinase 4 and/or 6 (CDK4/6) inhibitor plus endocrine therapy, as well as patients with triple-negative breast cancer luminal androgen receptor subtype (TNBC-LAR), is open for enrollment. Boundless expects to deliver initial safety and efficacy clinical proof-of-concept data within its existing cash runway timeline. POTENTIATE clinical trial of BBI-355 and BBI-825 In January 2026, Boundless announced its intention to cease enrollment in the Phase 1/2 POTENTIATE trial evaluating the combination of BBI-355 and BBI-825 based on market considerations, available clinical data, and prioritization of its BBI-940 program. Fourth Quarter and Full Year 2025 Financial Results Cash Position: Cash, cash equivalents, and short-term investments totaled $107.6 million as of December 31, 2025. The Company expects its cash to fund operations into the second half of 2028, through the anticipated initial clinical proof-of-concept readout from KOMODO-1. Research and Development (R&D) Expenses: R&D expenses were $9.8 million for the fourth quarter of 2025 and $44.8 million for the full year 2025, compared to $13.3 million and $55.3 million for the same periods of 2024. General and Administrative (G&A) Expenses: G&A expenses were $4.2 million for the fourth quarter of 2025 and $18.7 million for the full year 2025, compared to $5.0 million and $18.0 million for the same periods of 2024. Net Loss: Net loss totaled $12.9 million for the fourth quarter of 2025 and $58.2 million for the full year 2025, compared to $16.4 million and $65.4 million for the same periods of 2024. About Boundless Bio Boundless Bio is a clinical-stage oncology company dedicated to unlocking a new paradigm in cancer therapeutics that addresses the significant unmet need in patients with oncogene amplified tumors. Boundless Bio’s research focuses on extrachromosomal DNA (ecDNA), a root cause of oncogene amplification observed in 14% to 17% of cancer patients. Boundless Bio is developing BBI-940, a potentially first-in-class, oral, selective Kinesin degrader as an ecDNA-directed therapeutic candidate (ecDTx). Boundless Bio is headquartered in San Diego, CA. For more information, visit www.boundlessbio.com and follow us on LinkedIn and X. Forward-Looking Statements Boundless Bio (the Company) cautions you that statements contained in this press release that are not a description of historical facts are forward-looking statements. In some cases, you can identify forward-looking statements by terms such as “anticipate,” “believe,” “contemplate,” “continue,” “could,” “estimate,” “expect,” “intend,” “may,” “plan,” “potential,” “predict,” “project,” “should,” “would,” “target,” or “will” or the negative of these terms or other similar expressions. Forward-looking statements are based on the Company’s current beliefs and expectations and include but are not limited to statements regarding: the expected timing of an initial clinical proof-of-concept readout from the KOMODO-1 trial; the Company’s cash runway and the sufficiency thereof to fund operations through the anticipated initial clinical proof-of-concept readout from the KOMODO-1 trial; the potential safety and therapeutic benefits of BBI-940 and other ecDTx the Company may develop in treating patients with oncogene amplified cancers; the expected benefits of the Company’s portfolio prioritization, capital allocation, and revised operating plan; and the Company’s potential to deliver clinically-meaningful, high-impact ecDTx for cancer patients and create long-term value for stockholders. The Company’s actual results and performance may differ materially from those expressed or implied in any forward-looking statement due to substantial known and unknown risks and uncertainties, including, without limitation: potential delays in the enrollment, data readouts, or completion of clinical trials or in regulatory submissions and responses; the Company may use its capital resources sooner than it expects; the Company may be unable to obtain necessary additional funding when needed, on acceptable terms, or at all; the Company is early in its development efforts and its approach to discover and develop ecDTx to treat oncogene amplified cancers is novel and unproven; clinical and preclinical development of therapeutics involves a lengthy and expensive process with inherently uncertain timelines and outcomes; results from preclinical studies or early clinical trials not necessarily being predictive of future results; unexpected adverse side effects or inadequate efficacy of the Company’s ecDTx that may limit their development, regulatory approval, and/or commercialization; the Company’s ability to retain key personnel; the Company’s dependence on third parties in connection with clinical trials, preclinical studies, and manufacturing; the Company may expend its limited resources to pursue a particular ecDTx or combination therapy and fail to capitalize on ecDTx with greater development or commercial potential; the potential for the Company’s programs and prospects to be negatively impacted by developments relating to its competitors, including the results of studies or regulatory determinations relating to its competitors; regulatory and healthcare reform developments in the United States and foreign countries; disruptions in the FDA’s ability to perform routine activities or function in the normal course; the Company’s ability to obtain, maintain, defend, and enforce patent or other intellectual property protection for its ecDTx and technology; macroeconomic and geopolitical events and conditions, including international trade policies and tariffs; and other risks described in the Company’s filings with the Securities and Exchange Commission (SEC), including under the heading “Risk Factors” in the Company’s annual report on Form 10-K for the year ended December 31, 2025 and any subsequent filings with the SEC. You are cautioned not to place undue reliance on forward-looking statements, which speak only as of the date hereof, and, except as required by law, the Company undertakes no obligation to update such statements to reflect events that occur or circumstances that exist after the date hereof. All forward-looking statements are qualified in their entirety by this cautionary statement, which is made under the safe harbor provisions of the Private Securities Litigation Reform Act of 1995. Investor Contacts: James Lee, Boundless Bio, Inc. [email protected] Renee Leck, THRUST Strategic Communications [email protected] Media Contact: Carly Scaduto [email protected]

Enrollment ongoing in BBI-355 / BBI-825 combination arm of the POTENTIATE trial Investigational new drug submission for BBI-940 on track, with a first-in-human clinical trial expected to initiate in the first half of 2026 $118 million in cash supports operations into first half of 2028, through expected proof-of-concept clinical readouts for both programs SAN DIEGO, Nov. 05, 2025 (GLOBE NEWSWIRE) -- Boundless Bio (Nasdaq: BOLD), a clinical-stage oncology company interrogating extrachromosomal DNA (ecDNA) biology to deliver transformative therapies to patients with previously intractable oncogene amplified cancers, today announced financial results and business highlights for the fiscal quarter ended September 30, 2025. “We are advancing a pipeline rooted in tumor-enabling ecDNA biology to bring forward innovative therapies for patients with oncogene-amplified cancers,” said Zachary Hornby, President and Chief Executive Officer of Boundless Bio. “Enrollment is underway in the BBI-355/BBI-825 combination arm of the POTENTIATE trial, and we are excited to advance BBI-940, our novel, orally bioavailable Kinesin degrader into the clinic in the first half of 2026, as we work to deliver a meaningful impact for both patients and shareholders.” Research and Development Highlights and Upcoming Milestones POTENTIATE clinical trial of BBI-355 and BBI-825 The combination arm of the Phase 1/2 POTENTIATE trial evaluating BBI-355 and BBI-825 in oncogene-amplified cancers is actively enrolling. The Company expects to deliver initial proof-of-concept clinical data within its existing cash runway timeline. BBI-940 novel Kinesin program targeting ecDNA segregation and inheritance The Company expects to submit an investigational new drug (IND) application for BBI-940 and initiate a first-in-human Phase 1 clinical trial in the first half of 2026. Initial proof-of-concept clinical data are expected within the Company’s existing cash runway timeline. Third Quarter 2025 Financial Results Cash Position: Cash, cash equivalents, and short-term investments totaled $117.6 million as of September 30, 2025. Research and Development (R&D) Expenses: R&D expenses were $10.7 million for the third quarter of 2025, compared to $14.1 million for the same period in 2024. General and Administrative (G&A) Expenses: G&A expenses were $4.5 million for the third quarter of 2025, compared to $4.6 million for the same period in 2024. Net Loss: Net loss totaled $13.9 million for the third quarter of 2025, compared to $16.5 for the same period in 2024. About Boundless Bio Boundless Bio is a clinical-stage oncology company dedicated to unlocking a new paradigm in cancer therapeutics that addresses the significant unmet need in patients with oncogene amplified tumors. Boundless Bio’s research focuses on extrachromosomal DNA (ecDNA), a root cause of oncogene amplification, observed in 14% to 17% of cancer patients. Boundless Bio is developing the first ecDNA-directed therapeutic candidates (ecDTx), BBI-355, an oral, selective inhibitor of checkpoint kinase 1 (CHK1), and BBI-825, an oral, selective inhibitor of ribonucleotide reductase (RNR). These compounds are being evaluated in combination in patients with oncogene amplified cancers in the Company’s Phase 1/2 POTENTIATE clinical trial. Boundless Bio is conducting IND-enabling studies of another ecDTx, BBI-940, a potentially first-in-class, orally bioavailable, selective Kinesin degrader. Boundless Bio is headquartered in San Diego, CA. For more information, visit www.boundlessbio.com and follow us on LinkedIn and X. Forward-Looking Statements Boundless Bio (the Company) cautions you that statements included in this press release that are not a description of historical facts are forward-looking statements. In some cases, you can identify forward-looking statements by terms such as “anticipate,” “believe,” “contemplate,” “continue,” “could,” “estimate,” “expect,” “intend,” “may,” “plan,” “potential,” “predict,” “project,” “should,” “would,” “target,” or “will” or the negative of these terms or other similar expressions. These statements are based on the Company’s current beliefs and expectations. Forward-looking statements include statements regarding: the Company’s expected cash runway and the sufficiency thereof to fund operations through anticipated proof-of-concept clinical data readouts for each of its therapeutic programs; the timing of expected data readouts; submission of an IND application to the U.S. Food and Drug Administration (FDA) for and initiation of a Phase 1 clinical trial of BBI-940, and the timing thereof; the potential safety and therapeutic benefits of the Company’s ecDTx in treating patients with oncogene amplified cancers, including whether the combination of BBI-355 and BBI-825 will provide therapeutic benefit without overlapping toxicity; and the Company’s potential to deliver a meaningful impact for patients and shareholders. The Company’s actual results and performance may differ materially from those expressed or implied in any forward-looking statement due to substantial known and unknown risks and uncertainties, including, without limitation: the Company is early in its development efforts and its approach to discover and develop ecDTx to treat oncogene amplified cancers is novel and unproven; clinical and preclinical development of therapeutics involves a lengthy and expensive process with inherently uncertain timelines and outcomes; the Company’s ecDTx may not achieve favorable results in ongoing or future clinical trials; results from preclinical studies or early clinical trials not necessarily being predictive of future results; potential delays in the commencement, enrollment, data readouts or completion of clinical trials or preclinical studies or submission of an IND; the Company’s dependence on third parties in connection with clinical trials, preclinical studies, and manufacturing; unfavorable results from clinical trials or preclinical studies; the Company may expend its limited resources to pursue a particular ecDTx or combination therapy and fail to capitalize on ecDTx with greater development or commercial potential; unexpected adverse side effects or inadequate efficacy of the Company’s ecDTx that may limit their development, regulatory approval, and/or commercialization; the potential for the Company’s programs and prospects to be negatively impacted by developments relating to its competitors, including the results of studies or regulatory determinations relating to its competitors; regulatory and healthcare reform developments in the United States and foreign countries; disruptions in the FDA’s ability to perform routine activities or function in the normal course; the Company may use its capital resources sooner than it expects and be unable to obtain necessary additional funding when needed, on acceptable terms, or at all; the Company’s ability to obtain, maintain, defend, and enforce patent or other intellectual property protection for its ecDTx and technology; the potential for third-party claims of intellectual property infringement, misappropriation, or other violations against the Company; macroeconomic and geopolitical events and conditions, including international trade policies and tariffs; and other risks described in the Company’s filings with the Securities and Exchange Commission (SEC), including under the heading “Risk Factors” in the Company’s annual report on Form 10-K for the year ended December 31, 2024, the Company’s quarterly report on Form 10-Q for the quarterly period ended September 30, 2025, and any subsequent filings with the SEC. You are cautioned not to place undue reliance on forward-looking statements, which speak only as of the date hereof, and the Company undertakes no obligation to update such statements to reflect events that occur or circumstances that exist after the date hereof. All forward-looking statements are qualified in their entirety by this cautionary statement, which is made under the safe harbor provisions of the Private Securities Litigation Reform Act of 1995. Investor Contacts: James Lee, Boundless Bio, Inc. [email protected] Renee Leck, THRUST Strategic Communications [email protected] Media Contact: Carly Scaduto [email protected]

BBI-355 and BBI-825 combination arm of the POTENTIATE trial is now open for enrollment BBI-940 is on track for submission of an investigational new drug application in the first half of 2026 $127 million in cash supports operations into the first half of 2028, through expected proof-of-concept clinical readouts for both programs SAN DIEGO, Aug. 05, 2025 (GLOBE NEWSWIRE) -- Boundless Bio (Nasdaq: BOLD), a clinical-stage oncology company interrogating extrachromosomal DNA (ecDNA) biology to deliver transformative therapies to patients with previously intractable oncogene amplified cancers, today announced financial results and business highlights for the fiscal quarter ended June 30, 2025. “We are executing with sharpened focus on programs that we believe have the strongest scientific rationale and greatest potential to impact patients with oncogene-amplified cancers,” said Zachary Hornby, President and CEO of Boundless Bio. “We are excited to advance our BBI-355/BBI-825 combination in the clinic and to progress BBI-940, our development candidate in our novel kinesin program, toward IND submission, as we work to make a meaningful impact for both patients and shareholders.” Research and Development Highlights and Upcoming Milestones POTENTIATE clinical trial The Company believes recent preclinical data provide a strong mechanistic rationale to combine BBI-355, its novel, selective, oral CHK1 inhibitor, with BBI-825, its novel, selective, oral RNR inhibitor, for synergistic anti-tumor activity without overlapping toxicity, and with a dosing regimen that does not require continuous administration. The BBI-355/BBI-825 combination arm of the POTENTIATE trial is open for enrollment. The Company expects to deliver initial proof-of-concept clinical data within its existing cash runway timeline. Novel Kinesin program targeting ecDNA segregation and inheritance Boundless selected BBI-940 as its development candidate for its novel program targeting a previously undrugged kinesin. Boundless expects to submit an investigational new drug (IND) application for BBI-940 in the first half of 2026 and to deliver initial proof-of-concept clinical data within its existing cash runway timeline. Second Quarter 2025 Financial Results Cash Position: Cash, cash equivalents, and short-term investments totaled $127.1 million as of June 30, 2025. Research and Development (R&D) Expenses: R&D expenses were $12.2 million for the second quarter of 2025, compared to $14.7 million for the same period in 2024. General and Administrative (G&A) Expenses: G&A expenses were $4.8 million for the second quarter of 2025, compared to $4.7 million for the same period in 2024. Net Loss: Net loss totaled $15.7 million for the second quarter of 2025, compared to $17.0 for the same period in 2024. About Boundless Bio Boundless Bio is a clinical-stage oncology company dedicated to unlocking a new paradigm in cancer therapeutics that addresses the significant unmet need in patients with oncogene amplified tumors. Boundless Bio’s research focuses on extrachromosomal DNA (ecDNA), a root cause of oncogene amplification observed in 14% to 17% of cancer patients. Boundless Bio is developing the first ecDNA-directed therapeutic candidates (ecDTx), BBI-355, an oral, selective inhibitor of checkpoint kinase 1 (CHK1), and BBI-825, an oral, selective inhibitor of ribonucleotide reductase (RNR). These compounds are being evaluated in combination in patients with oncogene amplified cancers in the Company’s phase 1/2 POTENTIATE clinical trial. Boundless Bio is conducting IND-enabling studies of another ecDTx, BBI-940, a potentially first-in-class orally bioavailable, selective Kinesin degrader. Boundless Bio is headquartered in San Diego, CA. For more information, visit www.boundlessbio.com and follow us on LinkedIn and X. Forward-Looking Statements The Company cautions you that statements included in this report that are not a description of historical facts are forward-looking statements. In some cases, you can identify forward-looking statements by terms such as “anticipate,” “believe,” “contemplate,” “continue,” “could,” “estimate,” “expect,” “intend,” “may,” “plan,” “potential,” “predict,” “project,” “should,” “would,” “target,” or “will” or the negative of these terms or other similar expressions. These statements are based on the Company’s current beliefs and expectations. Forward-looking statements include statements regarding: the Company’s expected cash runway and the sufficiency thereof to fund operations through anticipated proof-of-concept clinical data readouts for each of its therapeutic programs; the timing of expected data readouts; submission of an IND application for BBI-940 and the timing thereof; the potential safety and therapeutic benefits of its ecDNA directed therapeutic candidates (ecDTx) in treating patients with oncogene amplified cancers, including whether the combination of BBI-355 and BBI-825 will provide therapeutic benefit without overlapping toxicity, and the potential positive impact for shareholders. Forward-looking statements are subject to risks and uncertainties inherent in the Company’s business, including, without limitation: the Company is early in its development efforts and its approach to discover and develop ecDTx to treat oncogene amplified cancers is novel and unproven; results from preclinical studies or early clinical trials not necessarily being predictive of future results; potential delays in the commencement, enrollment, data readouts or completion of clinical trials or preclinical studies or submission of an IND; its dependence on third parties in connection with clinical trials, preclinical studies, and manufacturing; unfavorable results from clinical trials or preclinical studies; the Company may expend its limited resources to pursue a particular ecDTx or combination therapy and fail to capitalize on ecDTx with greater development or commercial potential; unexpected adverse side effects or inadequate efficacy of its ecDTx that may limit their development, regulatory approval, and/or commercialization; the potential for the Company’s programs and prospects to be negatively impacted by developments relating to its competitors, including the results of studies or regulatory determinations relating to its competitors; regulatory developments in the United States and foreign countries; the Company may use its capital resources sooner than it expects; and other risks described in the Company’s filings with the Securities and Exchange Commission (SEC), including under the heading “Risk Factors” in the Company’s annual report on Form 10-K for the year ended December 31, 2024 and any subsequent filings with the SEC. You are cautioned not to place undue reliance on these forward-looking statements, which speak only as of the date hereof, and the Company undertakes no obligation to update such statements to reflect events that occur or circumstances that exist after the date hereof. All forward-looking statements are qualified in their entirety by this cautionary statement, which is made under the safe harbor provisions of the Private Securities Litigation Reform Act of 1995. Investor Contacts: James Lee, Boundless Bio, Inc. [email protected] Renee Leck, THRUST Strategic Communications [email protected] Media Contact: Carly Scaduto [email protected]

Initial proof-of-concept data from the ongoing BBI-355 Phase 1/2 POTENTIATE trial in patients with oncogene-amplified cancers anticipated in the second half of 2025 Novel Kinesin program on track for mid-2025 development candidate nomination and IND filing in the first half of 2026 $138 million cash position provides operating runway into 2027 SAN DIEGO, May 09, 2025 (GLOBE NEWSWIRE) -- Boundless Bio (Nasdaq: BOLD), a clinical-stage oncology company interrogating extrachromosomal DNA (ecDNA) biology to deliver transformative therapies to patients with previously intractable oncogene amplified cancers, today announced financial results and business highlights for the fiscal quarter ended March 31, 2025. “Boundless remains committed to delivering new therapeutic options to patients with high unmet need oncogene amplified cancers,” said Zachary Hornby, President and CEO of Boundless Bio. “We look forward to providing a clinical data update on our BBI-355 program later this year. Additionally, we expect to nominate a development candidate for our novel Kinesin program by mid-year, with plans to submit an IND in the first half of 2026." Research and Development Highlights and Upcoming Milestones BBI-355, a novel, oral, potent CHK1 inhibitor designed to target replication stress in oncogene-amplified cancers Enrollment is ongoing in the Phase 1/2 POTENTIATE trial. Preliminary clinical proof-of-concept safety and antitumor activity data are expected in the second half of 2025. Novel Kinesin program targeting ecDNA segregation and inheritance Boundless expects to nominate a development candidate for its preclinical program targeting a previously undrugged kinesin by mid-2025, with an investigational new drug (IND) submission planned for the first half of 2026. Recent Data Presentations Preclinical data from studies conducted with Boundless’s ribonucleotide reductase (RNR) inhibitor, BBI-825, were presented in an oral session at the American Association for Cancer Research (AACR) Annual Meeting. These data suggest that the combination of BBI-825 with mutant-specific, pan, and multi-RAS targeting inhibitors delayed or prevented acquired resistance in colorectal cancer preclinical models. Boundless continues to preclinically evaluate BBI-825 in various treatment settings. First Quarter 2025 Financial Results Cash Position: Cash, cash equivalents, and short-term investments totaled $138.3 million as of March 31, 2025. Research and Development (R&D) Expenses: R&D expenses were $12.1 million for the first quarter of 2025, compared to $13.1 million for the same period in 2024. General and Administrative (G&A) Expenses: G&A expenses were $5.2 million for the first quarter of 2025, compared to $3.8 million for the same period in 2024. Net Loss: Net loss totaled $15.8 million for the first quarter of 2025, compared to $15.4 for the same period in 2024. About Boundless BioBoundless Bio is a clinical-stage oncology company dedicated to unlocking a new paradigm in cancer therapeutics to address the significant unmet need of patients with oncogene amplified tumors. Boundless’s research focuses on extrachromosomal DNA (ecDNA), a root cause of oncogene amplification observed in 14 to 17% of cancer patients. Boundless Bio is developing the first ecDNA-directed therapeutic candidate (ecDTx), BBI-355, which is an oral inhibitor of checkpoint kinase 1 (CHK1) being evaluated in a Phase 1/2 clinical trial in patients with oncogene amplified cancers. Leveraging its Spyglass platform, Boundless Bio has additional ecDTx programs, including its novel Kinesin program, advancing through preclinical development and discovery. Boundless Bio is headquartered in San Diego, CA. For more information, visit www.boundlessbio.com and follow us on LinkedIn and X. Forward-Looking StatementsBoundless Bio cautions you that statements contained in this press release regarding matters that are not historical facts are forward-looking statements. The forward-looking statements are based on our current beliefs and expectations and include but are not limited to: the timing of expected preliminary clinical proof-of-concept data from the Phase 1/2 POTENTIATE trial, nomination of an ecDTx from the Kinesin program and submission of an IND application to the U.S. Food and Drug Administration (FDA) for that ecDTx, our anticipated cash runway and the sufficiency of our cash position to fund achievement of program milestones; the potential therapeutic applications and benefits of our ecDTx in treating patients with oncogene amplified cancers; our clinical and preclinical research and development plans for our ecDTx; and our ability to discover and develop new ecDTx. Our actual results and performance may differ materially from those expressed or implied in any forward-looking statement set forth in this press release due to numerous known and unknown risks and uncertainties, including, without limitation: we are early in our development efforts and our approach to discover and develop ecDTx directed against ecDNA in oncogene amplified cancers is novel and unproven; risks inherent in the business of discovering, developing, obtaining regulatory approval for, and commercializing drugs for use as human therapeutics and operating as an early clinical-stage company; we only have one ecDTx in clinical development and all of our other development efforts are in the discovery and preclinical development stage; results from preclinical studies or early clinical trials not necessarily being predictive of future results; potential delays in the commencement, enrollment, data readouts or completion of clinical trials or preclinical studies, or submission of an IND; final data from our clinical trials may be materially different from interim, topline or preliminary data we publish as more patient data become available and/or data undergo more comprehensive reviews and audit and verification procedures; analytical validation of our ecDNA diagnostic not necessarily being predictive of its clinical validity and utility; our dependence on third parties in connection with clinical trials, preclinical studies, ecDNA diagnostic development, and manufacturing; unfavorable results from clinical trials or preclinical studies; we may expend our limited resources to pursue a particular ecDTx and fail to capitalize on ecDTx with greater development or commercial potential; unexpected adverse side effects or inadequate efficacy of our ecDTx that may limit their development, regulatory approval, and/or commercialization; the potential for our programs and prospects to be negatively impacted by developments relating to our competitors, including the results of studies or regulatory determinations relating to our competitors; regulatory developments in the United States and foreign countries; disruptions in the FDA’s ability to perform routine activities or function in the normal course, including due to reduced staffing or funding levels, could result in longer review periods for our regulatory submissions and delay advancement of our ecDTx; we may use our capital resources sooner than we expect; we may be unable to obtain necessary additional funding when needed or on acceptable terms; the effect of macroeconomic and geopolitical events and conditions our business, operating costs, ability to raise additional capital, and stock price; and other risks described in our filings with the Securities and Exchange Commission (SEC), including under the heading “Risk Factors” in our annual report on Form 10-K for the year ended December 31, 2024 and any subsequent filings with the SEC. You are cautioned not to place undue reliance on these forward-looking statements, which speak only as of the date hereof, and we undertake no obligation to update such statements to reflect events that occur or circumstances that exist after the date hereof. All forward-looking statements are qualified in their entirety by this cautionary statement, which is made under the safe harbor provisions of the Private Securities Litigation Reform Act of 1995. Investor Contacts:Ben Flaum, Boundless [email protected] Renee Leck, THRUST Strategic Communications [email protected] Media Contact:Carly [email protected]

BBI-355 Phase 1/2 POTENTIATE trial ongoing in patients with oncogene amplified cancers, with initial proof of concept data expected in the second half of 2025 Novel Kinesin program progressing toward development candidate nomination by mid-2025, with IND submission expected in the first half of 2026 With a $152 million cash position at the end of 2024, Boundless projects operating runway into 2027 SAN DIEGO, March 27, 2025 (GLOBE NEWSWIRE) -- Boundless Bio (Nasdaq: BOLD), a clinical-stage oncology company interrogating extrachromosomal DNA (ecDNA) biology to deliver transformative therapies to patients with previously intractable oncogene amplified cancers, today announced financial results and business highlights for the fiscal quarter and full year ended December 31, 2024. “We made important strides in 2024 as we became a public company and continued to advance BBI-355, our oral, selective CHK1 inhibitor in the Phase 1/2 POTENTIATE trial in patients with oncogene amplified cancers, and we look forward to reporting preliminary proof-of-concept data in the second half of this year,” said Zachary Hornby, President and CEO of Boundless Bio. “Additionally, we have continued to identify new targets and are advancing an oral degrader of a novel kinesin identified by our Spyglass platform. We are on track to nominate a development candidate for our Kinesin program by mid-year, with the intention to submit an IND in the first half of 2026. We look forward to the year ahead as we continue to advance our pipeline to address the significant unmet need in patients with oncogene amplified cancers.” Research and Development Highlights and Upcoming Milestones BBI-355, a novel, oral, potent CHK1 inhibitor designed to target replication stress in oncogene-amplified cancers Enrollment in the Phase 1/2 POTENTIATE clinical trial evaluating BBI-355 as a monotherapy and combination agent in patients with locally advanced or metastatic solid tumors with oncogene amplifications is ongoing. ECHO, a proprietary diagnostic for the detection of ecDNA amplified oncogenes, is in use in the POTENTIATE trial. Boundless expects to report preliminary clinical proof-of-concept safety and antitumor activity data in the second half of 2025. Novel Kinesin program targeting ecDNA segregation and inheritance Boundless is advancing a preclinical program targeting a previously undrugged kinesin that is essential for proper ecDNA segregation and inheritance during cell division. Boundless expects to nominate a development candidate by mid-2025 and submit an investigational new drug application (IND) to the FDA in the first half of 2026. Recent Corporate Highlights In February 2025, Boundless appointed Robert Doebele, M.D., Ph.D., as Chief Medical Officer. Dr. Doebele is a medical oncologist and previously served as Chief Medical Officer and Chief Scientific Officer at Rain Oncology, where he led the early and late-stage development of multiple oncology programs using biology-based, tumor-agnostic strategies. Fourth Quarter and Full Year 2024 Financial Results Cash Position: Cash, cash equivalents, and short-term investments totaled $152.1 million as of December 31, 2024. Research and Development (R&D) Expenses: R&D expenses were $13.3 million for the fourth quarter of 2024 and $55.3 million for the full year 2024, compared to $10.4 million and $42.6 million for the same periods in 2023. General and Administrative (G&A) Expenses: G&A expenses were $5.0 million for the fourth quarter of 2024 and $18.0 million for the full year 2024, compared to $3.4 million and $12.2 million for the same periods in 2023. Net Loss: Net loss totaled $16.4 million for the fourth quarter of 2024 and $65.4 million for the full year 2024, compared to $12.1 million and $49.4 million for the same periods in 2023. About Boundless BioBoundless Bio is a clinical-stage oncology company dedicated to unlocking a new paradigm in cancer therapeutics to address the significant unmet need of patients with oncogene amplified tumors by targeting extrachromosomal DNA (ecDNA), a root cause of oncogene amplification observed in 14 to 17% of cancer patients. Boundless Bio is developing the first ecDNA-directed therapeutic candidate (ecDTx), BBI-355, which is an oral inhibitor of checkpoint kinase 1 (CHK1) being evaluated in a Phase 1/2 clinical trial in patients with oncogene amplified cancers. Leveraging its Spyglass platform, Boundless Bio has additional ecDTx programs advancing through preclinical development and discovery. Boundless Bio is headquartered in San Diego, CA. For more information, visit www.boundlessbio.com and follow us on LinkedIn and X. Forward-Looking StatementsBoundless Bio cautions you that statements contained in this press release regarding matters that are not historical facts are forward-looking statements. The forward-looking statements are based on our current beliefs and expectations and include but are not limited to: the timing of expected preliminary clinical proof-of-concept data from the Phase 1/2 POTENTIATE trial, nomination of an ecDTx from the Kinesin program and submission of an IND for that ecDTx, the sufficiency of our cash position to fund operations and achievement of program milestones; and the potential therapeutic benefits of our ecDTx in treating patients with oncogene amplified cancers. Our actual results and performance may differ materially from those expressed or implied in any forward-looking statement set forth in this press release due to numerous known and unknown risks and uncertainties, including, without limitation: we are early in our development efforts and our approach to discover and develop ecDTx directed against ecDNA in oncogene amplified cancers is novel and unproven; risks inherent in the business of discovering, developing, obtaining regulatory approval for, and commercializing drugs for use as human therapeutics and operating as an early clinical-stage company; we only have one ecDTx in clinical development and all of our other development efforts are in the discovery and preclinical development stage; results from preclinical studies or early clinical trials not necessarily being predictive of future results; potential delays in the commencement, enrollment, data readouts or completion of clinical trials or preclinical studies, or submission of an IND; final data from our clinical trials may be materially different from interim, topline or preliminary data we publish as more patient data become available and/or data undergo more comprehensive reviews and audit and verification procedures; analytical validation of our ecDNA diagnostic not necessarily being predictive of its clinical validity and utility; our dependence on third parties in connection with clinical trials, preclinical studies, ecDNA diagnostic development, and manufacturing; unfavorable results from clinical trials or preclinical studies; we may expend our limited resources to pursue a particular ecDTx and fail to capitalize on ecDTx with greater development or commercial potential; unexpected adverse side effects or inadequate efficacy of our ecDTx that may limit their development, regulatory approval, and/or commercialization; the potential for our programs and prospects to be negatively impacted by developments relating to our competitors, including the results of studies or regulatory determinations relating to our competitors; regulatory developments in the United States and foreign countries; disruptions in how the U.S. Food and Drug Administration (FDA) operates, including due to staff reductions, could result in longer review periods for our regulatory submissions and delay advancement of our ecDTx; we may use our capital resources sooner than we expect; and other risks described in our filings with the Securities and Exchange Commission (SEC), including under the heading “Risk Factors” in our annual report on Form 10-K for the year ended December 31, 2024 and any subsequent filings with the SEC. You are cautioned not to place undue reliance on these forward-looking statements, which speak only as of the date hereof, and we undertake no obligation to update such statements to reflect events that occur or circumstances that exist after the date hereof. All forward-looking statements are qualified in their entirety by this cautionary statement, which is made under the safe harbor provisions of the Private Securities Litigation Reform Act of 1995. Investor Contacts:Ben Flaum, Boundless [email protected] Renee Leck, THRUST Strategic Communications [email protected] Media Contact:Carly [email protected]