PART I. FINANCIAL INFORMATION [Financial Statements (Unaudited)](index=3&type=section&id=Item%201.%20Financial%20Statements%20(Unaudited)) Unaudited Q1 2024 financial statements show a **net loss of $15.4 million**, total assets at **$117.1 million**, **$15.8 million cash used in operations**, and a subsequent **$87.7 million IPO** [Condensed Balance Sheets](index=3&type=section&id=Condensed%20Balance%20Sheets) As of March 31, 2024, total assets decreased to **$117.1 million** from **$129.9 million** at year-end 2023, primarily due to reduced short-term investments, while the stockholders' deficit widened to **$141.2 million** Condensed Balance Sheet Summary (in thousands) | Account | March 31, 2024 (unaudited) | December 31, 2023 | | :--- | :--- | :--- | | **Assets** | | | | Cash and cash equivalents | $25,143 | $23,706 | | Short-term investments | $79,737 | $97,046 | | Total current assets | $112,161 | $124,204 | | **Total assets** | **$117,077** | **$129,894** | | **Liabilities & Stockholders' Deficit** | | | | Total current liabilities | $10,644 | $9,359 | | Convertible preferred stock | $247,617 | $247,617 | | Total stockholders' deficit | ($141,184) | ($127,082) | | **Total liabilities, convertible preferred stock, and stockholders' deficit** | **$117,077** | **$129,894** | [Condensed Statements of Operations and Comprehensive Loss](index=4&type=section&id=Condensed%20Statements%20of%20Operations%20and%20Comprehensive%20Loss) Q1 2024 net loss increased to **$15.4 million** from **$11.7 million** in Q1 2023, driven by higher operating expenses, particularly **R&D at $13.1 million** and **G&A at $3.8 million** Statement of Operations Summary (in thousands, except per share data) | Metric | Three Months Ended March 31, 2024 | Three Months Ended March 31, 2023 | | :--- | :--- | :--- | | Research and development | $13,129 | $9,503 | | General and administrative | $3,754 | $2,584 | | **Total operating expenses** | **$16,883** | **$12,087** | | Loss from operations | ($16,883) | ($12,087) | | Interest income | $1,421 | $395 | | **Net loss** | **($15,430)** | **($11,719)** | | Net loss per share, basic and diluted | ($12.27) | ($9.91) | [Condensed Statements of Cash Flows](index=6&type=section&id=Condensed%20Statements%20of%20Cash%20Flows) Q1 2024 saw **$15.8 million net cash used in operating activities**, **$18.1 million provided by investing activities**, and **$0.9 million used in financing activities**, resulting in a **$1.4 million net increase in cash** Cash Flow Summary (in thousands) | Cash Flow Activity | Three Months Ended March 31, 2024 | Three Months Ended March 31, 2023 | | :--- | :--- | :--- | | Net cash used in operating activities | ($15,776) | ($12,090) | | Net cash provided by investing activities | $18,137 | $22,166 | | Net cash provided by / (used in) financing activities | ($924) | $31 | | **Net increase in cash and cash equivalents** | **$1,437** | **$10,107** | [Notes to Condensed Financial Statements](index=7&type=section&id=Notes%20to%20Condensed%20Financial%20Statements) Notes detail the company's clinical-stage oncology focus, a March 2024 reverse stock split, an April 2024 IPO raising **$87.7 million**, and sufficient liquidity for at least 12 months - The company is a clinical-stage precision oncology firm developing small molecule drugs (ecDTx) targeting extrachromosomal DNA (ecDNA)[13](index=13&type=chunk) - On March 19, 2024, the company completed a **1-for-19.5 reverse stock split** of its common stock, with all share and per-share amounts retroactively adjusted[14](index=14&type=chunk) - On April 2, 2024, the company completed its IPO, raising approximately **$87.7 million in net proceeds**, with all outstanding convertible preferred stock converting into **14,740,840 shares of common stock** prior to the offering[66](index=66&type=chunk) - The company believes existing cash, cash equivalents, short-term investments, and IPO net proceeds will fund operations for at least **12 months** from the financial statement issuance date[16](index=16&type=chunk) [Management's Discussion and Analysis of Financial Condition and Results of Operations](index=24&type=section&id=Item%202.%20Management%27s%20Discussion%20and%20Analysis%20of%20Financial%20Condition%20and%20Results%20of%20Operations) Management discusses the company's ecDNA-directed therapeutics, including lead candidates BBI-355 and BBI-825 in Phase 1/2 trials, ongoing operating losses, and sufficient capital from the April 2024 IPO to fund operations into H2 2026 [Overview](index=24&type=section&id=Overview) Boundless Bio, a clinical-stage oncology company, focuses on ecDNA-targeted therapies, with lead candidates BBI-355 and BBI-825 in Phase 1/2 trials, and utilizes its proprietary Spyglass platform - Lead ecDTx, **BBI-355 (CHK1 inhibitor)**, is in the Phase 1/2 POTENTIATE clinical trial, with preliminary data expected in **H2 2024**[73](index=73&type=chunk) - Second ecDTx, **BBI-825 (RNR inhibitor)**, is in the Phase 1/2 STARMAP clinical trial, with preliminary data expected in **H2 2025**[74](index=74&type=chunk) - A third ecDTx program targeting a kinesin essential for ecDNA segregation is in discovery, with an IND submission planned for **H1 2026**[75](index=75&type=chunk) [Results of Operations](index=31&type=section&id=Results%20of%20Operations) Q1 2024 operating expenses increased to **$16.9 million**, with **R&D rising to $13.1 million** due to program costs and personnel, and **G&A growing to $3.8 million** from higher personnel and professional fees R&D Expense Breakdown (in thousands) | Expense Category | Q1 2024 | Q1 2023 | Change | | :--- | :--- | :--- | :--- | | **Direct Program Costs** | | | | | BBI-355 | $2,231 | $1,798 | $433 | | BBI-825 | $2,136 | $1,019 | $1,117 | | Other development programs | $1,220 | $1,011 | $209 | | **Total Direct Program Costs** | **$5,587** | **$3,828** | **$1,759** | | **Indirect Program Costs** | **$7,542** | **$5,675** | **$1,867** | | **Total R&D Expenses** | **$13,129** | **$9,503** | **$3,626** | - G&A expenses increased to **$3.8 million** in Q1 2024 from **$2.6 million** in Q1 2023, driven by higher personnel costs, stock-based compensation, and professional service fees[97](index=97&type=chunk) - Other income, net, increased by **$1.1 million** year-over-year, primarily due to higher interest income from Series C convertible preferred stock financing proceeds[98](index=98&type=chunk) [Liquidity and Capital Resources](index=32&type=section&id=Liquidity%20and%20Capital%20Resources) As of March 31, 2024, the company held **$104.9 million** in cash and investments, with the April 2024 IPO raising **$100.0 million** gross, providing sufficient capital to fund operations into **H2 2026** despite ongoing losses - As of March 31, 2024, the company held **$104.9 million** in cash, cash equivalents, and short-term investments[100](index=100&type=chunk) - In April 2024, the company completed its IPO, raising **$100.0 million** in gross proceeds[99](index=99&type=chunk) - Management believes IPO net proceeds combined with existing cash will fund operations into **H2 2026**[100](index=100&type=chunk) [Quantitative and Qualitative Disclosures About Market Risk](index=37&type=section&id=Item%203.%20Quantitative%20and%20Qualitative%20Disclosures%20About%20Market%20Risk) As a smaller reporting company, the company is not required to provide quantitative and qualitative disclosures about market risk - As a smaller reporting company, Boundless Bio is not required to provide quantitative and qualitative disclosures about market risk[113](index=113&type=chunk) [Controls and Procedures](index=37&type=section&id=Item%204.%20Controls%20and%20Procedures) Management concluded that disclosure controls and procedures were effective as of March 31, 2024, with internal control over financial reporting evaluation not yet required for the newly public company - Management concluded that disclosure controls and procedures were effective as of the end of the quarter[114](index=114&type=chunk) - The company is not yet required to have management evaluate the effectiveness of its internal control over financial reporting until the Annual Report for the year ending **December 31, 2025**[115](index=115&type=chunk) PART II. OTHER INFORMATION [Legal Proceedings](index=38&type=section&id=Item%201.%20Legal%20Proceedings) The company is not currently a party to any material legal proceedings, with ordinary course legal matters not expected to have a material adverse impact - The company is not currently a party to any material legal proceedings[117](index=117&type=chunk) [Risk Factors](index=38&type=section&id=Item%201A.%20Risk%20Factors) The company faces numerous risks including limited operating history, significant losses, dependence on future financing, unproven scientific approach, early-stage clinical programs, reliance on third parties, and intellectual property challenges - The company has a limited operating history, incurred **$151.5 million** in accumulated deficit as of March 31, 2024, and expects continued significant losses[120](index=120&type=chunk)[121](index=121&type=chunk) - The company's scientific approach of targeting ecDNA is novel and unproven, potentially hindering the development of commercially viable products[134](index=134&type=chunk) - The company relies on third parties for clinical trial conduct and ecDTx manufacturing, increasing performance, compliance, and supply risks[119](index=119&type=chunk)[179](index=179&type=chunk)[182](index=182&type=chunk) - Successful commercialization may depend on the development and regulatory approval of an ecDNA companion diagnostic, which carries inherent development and regulatory risks[160](index=160&type=chunk)[171](index=171&type=chunk) [Unregistered Sales of Equity Securities and Use of Proceeds](index=116&type=section&id=Item%202.%20Unregistered%20Sales%20of%20Equity%20Securities%20and%20Use%20of%20Proceeds) In Q1 2024, the company granted options for **1,375,088 common shares**, and its April 2, 2024 IPO generated approximately **$87.7 million in net proceeds**, with no material change to the planned use of funds - In Q1 2024, the company granted options to purchase **1,375,088 shares of common stock** at a weighted average exercise price of **$11.23 per share**[330](index=330&type=chunk) - The IPO on April 2, 2024, generated approximately **$87.7 million in net proceeds** after deducting **$7.0 million** in underwriting discounts and **$5.3 million** in other offering expenses[331](index=331&type=chunk) [Defaults Upon Senior Securities](index=118&type=section&id=Item%203.%20Defaults%20Upon%20Senior%20Securities) The company reports no defaults upon senior securities - The company reports no defaults upon senior securities[333](index=333&type=chunk) [Mine Safety Disclosures](index=118&type=section&id=Item%204.%20Mine%20Safety%20Disclosures) This item is not applicable to the company - This item is not applicable to the company[333](index=333&type=chunk) [Other Information](index=118&type=section&id=Item%205.%20Other%20Information) No officers or directors adopted, modified, or terminated Rule 10b5-1 or non-Rule 10b5-1 trading arrangements during Q1 2024 - No officers or directors adopted, modified, or terminated Rule 10b5-1 trading arrangements during the first quarter of 2024[333](index=333&type=chunk) [Exhibits](index=118&type=section&id=Item%206.%20Exhibits) This section lists exhibits filed with Form 10-Q, including corporate governance documents, equity plans, employment agreements, and Sarbanes-Oxley Act officer certifications - Lists key corporate documents, including the Amended and Restated Certificate of Incorporation, Bylaws, and various equity incentive plans[335](index=335&type=chunk) - Includes required certifications from the Principal Executive Officer and Principal Financial Officer pursuant to Sections 302 and 906 of the Sarbanes-Oxley Act[335](index=335&type=chunk)

Exhibit 99.1 Boundless Bio Reports First Quarter 2024 Financial Results and Corporate Highlights BBI-355 Phase 1/2 POTENTIATE clinical trial ongoing; initiated targeted therapy combinations in patients with tumors with EGFR or FGFR oncogene amplifications First patient dosed in Phase 1/2 STARMAP clinical trial of BBI-825 in patients with tumors with resistance gene amplifications Completed $100 million IPO; pro forma cash position of approximately $200 million supports both BBI-355 and BBI-825 through preli ...