Boundless Bio, Inc.

Organization and Basis of Presentation

Description of Business

Boundless Bio, Inc. (the Company) 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 by interrogating extrachromosomal DNA (ecDNA), a root cause of oncogene amplification observed in 14 to 17% of cancer patients. The Company is focused on identifying targets essential for ecDNA functionality in oncogene amplified cancer cells, then designing and developing small molecule drugs called ecDNA-directed therapeutic candidates (ecDTx) to inhibit those targets, with the aim to prevent cancer cells from using chromosomal instability and ecDNA amplification biology to grow, adapt, and become resistant to existing therapies. The Company's mission is to be the foremost biopharma company interrogating ecDNA biology to deliver transformative therapies that improve and extend the lives of patients with previously intractable oncogene amplified cancers. The Company’s lead ecDTx, BBI-940, is in early clinical development in patients with estrogen receptor positive and human epidermal growth factor receptor 2 negative, or ER+/HER2-, breast cancer who have progressed following treatment with a cyclin-dependent kinase 4 and/or 6 inhibitor, or CDK4/6 inhibitor, plus endocrine therapy, as well as patients with triple-negative breast cancer luminal androgen receptor subtype, or TNBC-LAR. The Company was incorporated in the state of Delaware on April 10, 2018 and is headquartered in San Diego, California.

ATM Offering

On April 1, 2025, the Company entered into an Open Market Sale Agreement SM (the Sales Agreement) with Jefferies LLC (the Agent), under which the Company may, from time to time, sell shares of the Company’s common stock in “at the market” (ATM) offerings through or to the Agent, as sales agent or principal. The shares of common stock will be offered and issued pursuant to the Company’s shelf registration statement on Form S-3 (File No. 333-286302), including the Sales Agreement prospectus contained therein, filed with the Securities and Exchange Commission (SEC) on April 1, 2025 and declared effective by the SEC on April 10, 2025. Pursuant to the Sales Agreement prospectus, the Company may sell shares of its common stock having an aggregate offering price of up to $14.5 million. Sales of the shares of common stock, if any, will be made at prevailing market prices at the time of sale, or as otherwise agreed with the Agent. The Agent will receive a commission from the Company of up to 3.0% of the gross proceeds of any shares of common stock sold under the Sales Agreement. The Company is not obligated to sell, and the Agent is not obligated to buy or sell, any shares of common stock under the Sales Agreement. No assurance can be given that the Company will sell any shares of common stock under the Sales Agreement, or, if it does, as to the price or amount of shares of common stock that it sells or the dates when such sales will take place. As of March 31, 2026, no shares had been sold under the Sales Agreement.

Liquidity

Since the Company commenced operations in 2018, it has devoted substantially all of its efforts and resources to organizing and staffing the Company, business planning, raising capital, building its proprietary Spyglass platform, discovering its ecDTx, developing its ecDNA diagnostic, establishing its intellectual property portfolio, conducting research, preclinical studies, and clinical trials, establishing arrangements with third parties for the manufacture of its ecDTx and related raw materials, and providing other general and administrative support for these operations. The Company does not have any products for sale and has not generated any revenue to date. The Company has funded its operations primarily from the sale and issuance of shares of its convertible preferred stock and common stock, including the net proceeds from the initial public offering (IPO) of its common stock completed on April 2, 2024.

As of March 31, 2026, the Company had cash, cash equivalents, and short-term investments of $92.8 million. Subsequent to March 31, 2026, the Company entered into an agreement with the landlord for its current headquarters facility to terminate the lease for such facility effective May 31, 2026. The lease termination involved a $10.0 million payment by the Company to the landlord and the landlord retained the Company's security deposit of approximately $0.5 million, representing aggregate cash outflows of approximately $10.5 million paid in the second quarter of 2026. After taking into account the foregoing, the Company believes that its existing cash, cash equivalents, and short-term investments will be sufficient to fund its operations for at least twelve months from the issuance date of the accompanying unaudited condensed financial statements. See Note 13 – Subsequent Events for additional information regarding the lease termination.

Since inception, the Company has incurred significant operating losses and negative cash flows from its operations and expects that it will continue to do so into the foreseeable future as it continues its development of, seeks regulatory approval for, and potentially commercializes its ecDTx, utilizes third parties to manufacture its ecDTx and related raw materials, potentially identifies additional development opportunities for its ecDTx, seeks to expand its therapeutic pipeline, and expands and protects its intellectual property. If the Company obtains regulatory approval for any of its ecDTx, it expects to incur significant commercialization expenses related to product sales, marketing, manufacturing, and distribution. The Company does not expect to generate any revenue from product sales untilit successfully completes development of and obtains regulatory approval for one or more of its ecDTx, which the Company expects will take several years and may never occur. As of March 31, 2026, the Company had an accumulated deficit of $273.2 million, and, during the three months ended March 31, 2026, the Company incurred a net loss of $13.6 million and had negative cash flows from operations of $15.0 million. As the Company continues to pursue its business plan, it will need to acquire a substantial amount of additional funding until such time as it is able to generate significant revenues to fund its research and development activities and operations. Accordingly, the Company expects to finance its cash requirements through equity offerings, debt financings, or other capital sources, including potential collaborations, licenses, and other similar arrangements. There can be no assurance that the Company will be successful in acquiring additional funding or that any additional funding would be sufficient to continue operations in future periods.

Basis of Presentation

The accompanying unaudited condensed financial statements have been prepared in accordance with United States generally accepted accounting principles (U.S. GAAP) and the requirements of the SEC for interim reporting. As permitted under those rules, certain footnote disclosures or other financial information that are normally required by U.S. GAAP have been condensed or omitted. The condensed financial statements are presented in U.S. dollars. Any reference in these notes to applicable guidance is meant to refer to U.S. GAAP as found in the Accounting Standards Codification (ASC) and Accounting Standards Updates (ASU) promulgated by the Financial Accounting Standards Board (FASB).

The condensed balance sheet as of March 31, 2026, the condensed statements of operations and comprehensive loss for the three months ended March 31, 2026 and 2025, the condensed statements of stockholders’ equity for the three months ended March 31, 2026 and 2025, and the condensed statements of cash flows for the three months ended March 31, 2026 and 2025 are unaudited. These unaudited condensed financial statements have been prepared on the same basis as the annual financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary to present fairly the Company’s financial position, results of operations, and cash flows for the interim period presented. The financial data and the other financial information contained in these notes to the condensed financial statements are also unaudited. The results of operations for the three months ended March 31, 2026 are not necessarily indicative of the results to be expected for the year ending December 31, 2026 or for any other future annual or interim period. The condensed balance sheet as of December 31, 2025 included herein was derived from the audited financial statements as of that date. The unaudited condensed financial statements and these notes thereto should be read in conjunction with the Company’s audited financial statements and the notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2025 filed with the SEC on March 9, 2026 (the Company's 2025 10-K).

Summary of Significant Accounting Policies

The Company’s significant accounting policies are disclosed in Note 2 to the audited financial statements included in the Company’s 2025 10-K. There were no material changes to the Company’s significant accounting policies during the three months ended March 31, 2026.

The Company qualifies as an “emerging growth company” (EGC) as defined in the Jumpstart Our Business Startups Act of 2012, as amended (JOBS Act). The JOBS Act permits EGCs such as the Company to take advantage of an extended transition period to comply with new or revised financial accounting standards applicable to public companies until those standards would otherwise apply to nonpublic companies. The Company has elected not to “opt out” of such extended transition period, which means that when an accounting standard is issued or revised and it has different application dates for public or nonpublic companies, the Company can adopt the new or revised standard at the time nonpublic companies adopt the new or revised standard and can do so until such time that it either (i) irrevocably elects to “opt out” of such extended transition period or (ii) no longer qualifies as an EGC.

Segment Reporting

Operating segments are identified as components of an enterprise about which discrete financial information is available for evaluation by the chief operating decision-maker (CODM) in making decisions regarding resource allocation and assessing performance. The Company operates and manages its business asone reporting andone operating segment, which is the business of designing and developing ecDTx, for which no revenue has been recorded. All of the Company’s long-lived assets are located in the United States. The Company’s CODM is its Chief Executive Officer. For purposes of assessing the Company’s financial performance and making resource allocation decisions, the CODM reviews total expenses, as well as expenses by nature.

Recent Accounting Pronouncements Not Yet Adopted

In November 2024, the FASB issued ASU No. 2024-03, Income Statement—Reporting Comprehensive Income—Expense Disaggregation Disclosures (Subtopic 220-40): Disaggregation of Income Statement Expenses. The new guidance requires more detailed information about specified types of expenses (including purchases of inventory, employee compensation, depreciation, amortization, and depletion) in commonly presented expense captions on the face of the statement of operations on an annual and interim basis. This guidance is effective for the Company for annual periods beginning after December 15, 2026, and interim periods beginning after December 15, 2027. The new standard permits early adoption and can be applied prospectively or retrospectively. The Company is evaluating the effect that this guidance will have on its financial statements and related disclosures.

Fair Value Measurements

The following tables summarize the Company’s financial assets measured at fair value on a recurring basis and their respective input levels based on the fair value hierarchy described in Note 2 to the audited financial statements included in the Company’s 2025 10-K (in thousands):

(1)

Included in cash and cash equivalents on the balance sheets.

(2)

Included in short-term investments on the balance sheets.

(1)

Included in cash and cash equivalents on the balance sheets.

(2)

Included in short-term investments on the balance sheets.

The Company’s money market funds are classified as Level 1 because they are valued using quoted market prices. The Company’s investments consist of available-for-sale securities and are classified as Level 2 because their value is based on valuations using significant inputs derived from or corroborated by observable market data. No Level 3 assets were held during the periods presented.

There wereno transfers of assets between fair value levels for any period presented.

Investments

The following tables summarize investments accounted for as available-for-sale securities (in thousands):

On March 31, 2026 and December 31, 2025, the remaining contractual maturities of all the Company’s available-for-sale investments were less than 12 months. As of March 31, 2026 and December 31, 2025, the Company has not established an allowance for credit losses for any of its available-for-sale securities.

As of March 31, 2026, there were fifteen available-for-sale securities with an estimated fair value of $48.9 million in gross unrealized loss positions. As of December 31, 2025, there wereno available-for-sale securities in a gross unrealized loss position. Based on its review of these investments, the Company believes that the unrealized losses are attributable to changes in market interest rates and not to credit-related factors and therefore were not other-than-temporary in nature.

Property and Equipment

Property and equipment, net consisted of the following (in thousands):

Depreciation and amortization expense related to property and equipment was $0.3 million for both the three months ended March 31, 2026 and 2025.

Accounts Payable and Accrued Liabilities

Accounts payable and accrued liabilities consisted of the following (in thousands):

Lease Agreements

2024 Lease

The Company is a party to a non-cancellable facility lease for approximately 80,168 square feet of lab and office space in San Diego, California (the 2024 Lease). In April 2026, the Company and the landlord entered into an agreement to terminate the 2024 Lease effective May 31, 2026. See Note 13 — Subsequent Events for a description of the lease termination. The following description reflects the terms of the 2024 Lease as they existed during the three months ended March 31, 2026 and as of March 31, 2026.

The 2024 Lease had an initial lease term of 120 months, which commenced in November 2024; the lease also provided the Company with the right to extend the lease term for an additional 60 months at expiry, which was not included in the lease term used for measurement. The 2024 Lease includes obligations to make base rent payments and additional variable lease payments for the Company’s allocated share of variable costs associated with the operation and management of the property, which include utilities, property taxes, common area maintenance, and amenities costs. The lease provided for a rent abatement period through July 2025.

The Company is required to maintain a security deposit under the 2024 Lease in the form of a standby letter-of-credit. This letter of credit is collateralized by a restricted cash deposit at the Company’s bank of approximately $0.6 million, which is included in restricted cash in the balance sheet. The 2024 Lease does not contain any material residual value guarantees or material restrictive financial covenants. The table below sets forth the Company’s future undiscounted operating lease payment obligations under the 2024 Lease as of March 31, 2026, exclusive of future variable lease costs. As noted above, the 2024 Lease was terminated effective May 31, 2026, and the obligations reflected in the table below with respect to amounts payable after May 31, 2026 will not be paid.

The Company recorded an operating lease liability for this obligation based on the present value of the lease payments using an estimated incremental borrowing rate of approximately 8.3%, as the 2024 Lease does not have a stated rate and the implicit rate was not readily determinable, and a right-of-use (ROU) asset based on the corresponding operating lease liability. Management exercised judgment in estimating the incremental borrowing rate and in determining the lease term. The renewal option was evaluated at lease commencement and excluded from the lease term, as the Company is not reasonably certain to exercise the option. The net ROU asset and associated lease liability are reflected in the Company’s balance sheet as of March 31, 2026 and December 31, 2025.

Operating leases

As of March 31, 2026, the 2024 Lease was the Company’s only lease. Lease expense related to the 2024 Lease totaled approximately $2.5 million and $2.3 million for the three months ended March 31, 2026 and 2025, respectively, and included operating lease costs of $1.8 million and $1.9 million, and variable lease costs of $0.7 million and $0.4 million, respectively.

The Company paid $1.7 million and $0.1 million for the operating lease included in the operating activities section of the condensed statements of cash flows for the three months ended March 31, 2026 and 2025, respectively. The remaining lease term and discount rate for the 2024 Lease were 8.6 years and 8.3%, respectively, as of March 31, 2026, and 8.8 years and 8.3%, respectively, as of December 31, 2025 (the calculations of remaining lease term excludes the renewal option). Future undiscounted operating lease payments under the 2024 Lease as of March 31, 2026, exclusive of future variable lease payments, were as follows (in thousands):

The table above reflects the Company’s contractual obligations under the 2024 Lease as of March 31, 2026. Subsequent to March 31, 2026, the Company and the landlord entered into an agreement to terminate the 2024 Lease effective May 31, 2026. As a result, other than the obligations payable through May 31, 2026, the obligations reflected in the table above will not be paid. See Note 13 — Subsequent Events for additional information regarding the lease termination and the Company’s new headquarters lease.

Commitments and Contingencies

Contracts

The Company enters into contracts in the normal course of business with various third parties for preclinical research studies, clinical trials, testing, manufacturing, and other services. These contracts generally provide for termination upon notice and are cancellable without significant penalty or payment and do not contain any minimum purchase commitments.

Indemnification Agreements

In the ordinary course of business, the Company may provide indemnification of varying scope and terms to vendors, lessors, business partners, and other parties with respect to certain matters including, but not limited to, losses arising out of breach of agreements or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with its officers and members of its board of directors that require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as officers or directors. The maximum potential future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. To date, the Company has not incurred any material costs because of these indemnification agreements. The Company has not accrued any liabilities related to such indemnification agreements in its financial statements as of March 31, 2026 or December 31, 2025 because it determined the likelihood of incurring a payment obligation pursuant to such agreements was not probable.

Litigation

Liabilities for loss contingencies arising from claims, assessments, litigation, fines, penalties, and other sources are recorded when it is probable that a liability has been incurred and the amount can be reasonably estimated. There are no matters currently outstanding for which any liabilities have been accrued. The Company was not a defendant in any lawsuit for the three months ended March 31, 2026 or the year ended December 31, 2025.

Common Stock

Common Stock Reserved for Future Issuance

Common stock reserved for future issuance consisted of the following (in thousands):

Stock-Based Compensation

Equity Incentive Plan

In March 2024, the Company’s board of directors adopted, and the Company’s stockholders approved, the 2024 Incentive Award Plan (the Plan), which became effective in connection with the IPO and has a term often years. As of March 31, 2026, a total of 5,068,078 shares of common stock were authorized for issuance under the Plan, which includes a January 1, 2026 increase of 1,120,362 shares, pursuant to the evergreen provision of the Plan. See Note 10 to the audited financial statements included in the Company’s 2025 10-K for a description of the evergreen provision of the Plan. On March 31, 2026,2,764,307 of these shares were available for grant under the Plan.

Prior to the adoption of the Plan, the Company had awarded common stock options under the 2018 Equity Incentive Plan (as amended, the Predecessor Plan). Under the provisions of the Plan, the shares subject to awards issued under the Predecessor Plan that were outstanding as of March 27, 2024, the effective date of the Plan, and that are subsequently cancelled or forfeited, will become available for issuance under, and will increase the number of shares that may be issued under, the Plan.

Repricing of Outstanding Options

In August 2024, the compensation committee of the Company’s board of directors, as administrator of the Plan and the Predecessor Plan, approved an option repricing (2024 Repricing), which was effective on August 19, 2024 (the Repricing Effective Date). The repricing applied to options to purchase up to an aggregate of 3,484,346 shares of the Company’s common stock with an exercise price per share in excess of the closing price per share of the Company’s common stock on the Repricing Effective Date, held by eligible employees of the Company that were granted under the Plan or the Predecessor Plan and were outstanding as of the Repricing Effective Date (the Repriced Options). As of March 31, 2026, Repriced Options to purchase up to an aggregate of 2,275,372 shares of the Company’s common stock remained outstanding. See Note 10 to the audited financial statements included in the Company’s 2025 10-K for a description of the 2024 Repricing.

Stock Options

Stock option activity under the Plan and the Predecessor Plan and certain other related information is as follows (in thousands except weighted-average exercise price and remaining term):

Aggregate intrinsic value in the above table is the difference between the estimated fair value of the Company’s common stock as of either March 31, 2026 or December 31, 2025, and the exercise price of stock options that had exercise prices below that value.

For the Repriced Options, the weighted-average prices and intrinsic value information in the table above is calculated based on the exercise price per share that applied immediately prior to the Repricing Effective Date pending satisfaction of the requisite service requirement or other service conditions.

No options were exercised during the three months ended March 31, 2026 or 2025.

Employee Stock Purchase Plan

In March 2024, the Company’s board of directors adopted, and the Company’s stockholders approved, the Company’s 2024 Employee Stock Purchase Plan (ESPP), which became effective in connection with the IPO. A total of 231,919 shares of common stock were initially reserved for issuance under the ESPP. On January 1, 2026, pursuant to the evergreen provision of the ESPP, the aggregate number of shares that may be issued under the ESPP was automatically increased by 224,072 shares. See Note 10 to the audited financial statements included in the Company’s 2025 10-K for a description of the ESPP, including the evergreen provision of the ESPP. On March 31, 2026, there were 527,251 shares available for issuance under the ESPP.

The Company recognized stock-based compensation expense related to the ESPP of $0.1 million for each of the three months ended March 31, 2026 and 2025.

The Company did not issue or sell any shares under the ESPP during the three months ended March 31, 2026 or 2025, respectively.

Stock-Based Compensation Expense

Stock-based compensation expense, including the expense related to the ESPP, as recorded in the accompanying condensed statements of operations and comprehensive loss was as follows (in thousands):

As of March 31, 2026, unrecognized compensation cost related to outstanding stock options (all of which have time-based vesting) was $9.5 million, which is expected to be recognized over a weighted-average period of 2.2 years.

As of March 31, 2026, unrecognized compensation cost related to the ESPP was $0.4 million, which is expected to be recognized as expense over approximately 1.1 years.

Excluding any effect of the Repriced Options, except for Repriced Options held by employees who experienced a Qualifying Termination (as defined in Note 10 to the audited financial statements included in the Company’s 2025 10-K), the weighted-average assumptions used in the Black-Scholes option pricing model to determine the fair value of the stock options granted during the periods indicated in the table were as follows:

Excluding any effect due to the Repriced Options, except for Repriced Options held by employees who experienced a Qualifying Termination, the weighted-average grant date per share fair value of options granted during the three months ended March 31, 2026 and 2025 were $1.04 and $2.09, respectively.

Net Loss Per Common Share

The following table summarizes the calculation of basic and diluted net loss per common share attributable to common stockholders (in thousands, except per share data):

The Company excluded the following potential shares of its common stock, presented based on amounts outstanding at each period end, from the calculation of diluted net loss per share for the periods indicated because including them would have had an anti-dilutive effect (in thousands):

Segment Information

The CODM reviews the budget versus actual expense by nature of expense. The following table sets forth the Company’s segment loss disclosure for the three months ended March 31, 2026 and 2025 (in thousands):

(1)

Includes expenses such as software licenses, database subscriptions, lab service contracts, travel, and other costs.

(2)

Includes expenses such as travel, investor relations services, software licenses, employee training and development, and other costs.

Subsequent Events

On April 13, 2026, the Company entered into an agreement with the landlord pursuant to which the parties agreed to terminate the 2024 Lease. The 2024 Lease was originally scheduled to expire on October 31, 2034. The lease will be terminated effective as of May 31, 2026. In connection with the lease termination, the Company paid $10.0 million to the landlord, and the landlord retained the Company's security deposit of approximately $0.5 million. Upon the effective termination date, the Company will also derecognize the right-of-use asset and operating lease liability associated with the 2024 Lease. In connection with the lease termination, the Company expects to recognize charges of approximately $2.4 million in the three months ending June 30, 2026 related to the accelerated depreciation of leasehold improvements and the abandonment of other building-related fixed assets pursuant to the lease termination agreement.

On April 17, 2026, the Company entered into a non-cancellable facility lease for approximately 10,822 rentable square feet of laboratory and office space located in La Jolla, California (2026 Lease). The 2026 Lease has an initial term of 12 months, commencing on June 1, 2026. The 2026 Lease also provides the Company with the option to extend the lease term for an additional 12 months. The 2026 Lease includes obligations to make monthly base rent payments of approximately $56,000, as well as additional variable lease payments representing the Company's allocated share of variable costs associated with the operation and management of the property, including utilities, property taxes, common area maintenance, and amenities costs. The 2026 Lease provides for two months of rent abatement during the second and third full calendar months of the initial lease term. The Company has provided a cash security deposit of approximately $77,000 under the 2026 Lease.