Organization and Basis of Presentation	6 Months Ended
Jun. 30, 2024
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Basis of Presentation	1. Organization and Basis of Presentation Description of Business Boundless Bio, Inc. (the Company) is a clinical-stage precision oncology company dedicated to unlocking a new paradigm in cancer therapeutics to address the significant unmet need in patients with oncogene amplified tumors by targeting extrachromosomal DNA (ecDNA). The Company is focused on designing and developing small molecule drugs called ecDNA directed therapeutic candidates (ecDTx). The Company was incorporated in the state of Delaware on April 10, 2018 and is headquartered in San Diego, California. Initial Public Offering On April 2, 2024, the Company completed its initial public offering (IPO), pursuant to which it sold 6,250,000 shares of its common stock at a public offering price of $16.00 per share, resulting in net proceeds of approximately $87.7 million, after deducting underwriting discounts, commissions, and other offering expenses. Immediately prior to the closing of the IPO, the Company’s outstanding convertible preferred stock automatically converted into 14,740,840 shares of common stock. Following the closing of the IPO, no shares of convertible preferred stock were authorized or outstanding. In connection with the closing of its IPO, on April 2, 2024, the Company’s certificate of incorporation was amended and restated to authorize 700,000,000 shares of common stock, par value $0.0001 per share and 70,000,000 shares of undesignated preferred stock, par value of $0.0001 per share. Reverse Stock Split On March 19, 2024, the Company effected a one-for-19.5 reverse stock split of its issued and outstanding shares of common stock. Accordingly, all share and per share amounts for all periods presented in the accompanying financial statements and notes thereto have been adjusted retroactively, where applicable, to reflect this reverse stock split and adjustment of the conversion ratios for each series of the Company’s convertible preferred stock. The par value and the number of authorized shares of the convertible preferred stock and common stock were not adjusted in connection with the reverse stock split. 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 candidate, 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. 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 any of its ecDTx and seeks to discover and develop additional ecDTx, utilizes third parties to manufacture its ecDTx and related raw materials, seeks to develop its ecDNA diagnostic candidate, hires additional personnel, 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. As of June 30, 2024, the Company had an accumulated deficit of $168.5 million and cash, cash equivalents, and short-term investments of $179.3 million. The Company believes that its existing cash, cash equivalents, and short-term investments will be sufficient to fund its operations for at least 12 months from the issuance date of these condensed financial statements. Basis of Presentation The accompanying financial statements have been prepared in accordance with U.S. generally accepted accounting principles (U.S. GAAP) and the requirements of the Securities and Exchange Commission (SEC) for interim reporting. As permitted under those rules, certain footnotes or other financial information that are normally required by GAAP can be condensed or omitted. The 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).

Organization and Basis of Presentation

6 Months Ended

Jun. 30, 2024

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Description of Business

Boundless Bio, Inc. (the Company) is a clinical-stage precision oncology company dedicated to unlocking a new paradigm in cancer therapeutics to address the significant unmet need in patients with oncogene amplified tumors by targeting extrachromosomal DNA (ecDNA). The Company is focused on designing and developing small molecule drugs called ecDNA directed therapeutic candidates (ecDTx). The Company was incorporated in the state of Delaware on April 10, 2018 and is headquartered in San Diego, California.

Initial Public Offering

On April 2, 2024, the Company completed its initial public offering (IPO), pursuant to which it sold 6,250,000 shares of its common stock at a public offering price of $16.00 per share, resulting in net proceeds of approximately $87.7 million, after deducting underwriting discounts, commissions, and other offering expenses. Immediately prior to the closing of the IPO, the Company’s outstanding convertible preferred stock automatically converted into 14,740,840 shares of common stock. Following the closing of the IPO, no shares of convertible preferred stock were authorized or outstanding.

In connection with the closing of its IPO, on April 2, 2024, the Company’s certificate of incorporation was amended and restated to authorize 700,000,000 shares of common stock, par value $0.0001 per share and 70,000,000 shares of undesignated preferred stock, par value of $0.0001 per share.

Reverse Stock Split

On March 19, 2024, the Company effected a one-for-19.5 reverse stock split of its issued and outstanding shares of common stock. Accordingly, all share and per share amounts for all periods presented in the accompanying financial statements and notes thereto have been adjusted retroactively, where applicable, to reflect this reverse stock split and adjustment of the conversion ratios for each series of the Company’s convertible preferred stock. The par value and the number of authorized shares of the convertible preferred stock and common stock were not adjusted in connection with the reverse stock split.

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 candidate, 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.

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 any of its ecDTx and seeks to discover and develop additional ecDTx, utilizes third parties to manufacture its ecDTx and related raw materials, seeks to develop its ecDNA diagnostic candidate, hires additional personnel, 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. As of June 30, 2024, the Company had an accumulated deficit of $168.5 million and cash, cash equivalents, and short-term investments of $179.3 million. The Company believes that its existing cash, cash equivalents, and short-term investments will be sufficient to fund its operations for at least 12 months from the issuance date of these condensed financial statements.

Basis of Presentation

The accompanying financial statements have been prepared in accordance with U.S. generally accepted accounting principles (U.S. GAAP) and the requirements of the Securities and Exchange Commission (SEC) for interim reporting. As permitted under those rules, certain footnotes or other financial information that are normally required by GAAP can be condensed or omitted. The 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).