Organization and Basis of Presentation	6 Months Ended
Jun. 30, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Basis of Presentation	1. Organization and Basis of Presentation Organization Calithera Biosciences, Inc., or the Company, was incorporated in the State of Delaware on March 9, 2010. The Company is a fully-integrated, clinical stage precision oncology biopharmaceutical company. Driven by a commitment to rigorous science and a passion for improving the lives of people impacted by cancer, Calithera is advancing a pipeline of investigational, small molecule oncology compounds with a biomarker-driven approach. The Company’s principal operations are based in South San Francisco, California, and it operates in one segment. Presentation The condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries, Calithera Biosciences UK Limited and Calithera Biosciences Ireland Limited. All significant intercompany accounts and transactions have been eliminated from the condensed consolidated financial statements. The Company's Ability to Continue as a Going Concern As of June 30, 2022, the Company had cash and cash equivalents of $41.8 million. The Company has incurred losses since inception and to date has financed its operations primarily through the sale of shares of its capital stock and payments from the Company’s collaboration and licensing agreements. As of June 30, 2022, the Company had an accumulated deficit of $495.9 million. During the year ended December 31, 2021 and six months ended June 30, 2022, the Company incurred a loss from continuing operations of $115.1 million and $22.9 million, respectively, and used $66.3 million and $27.3 million of cash in operations, respectively. The Company expects to continue to generate operating losses and negative operating cash flows for the foreseeable future and will need additional funding to support its planned operating activities through profitability. The transition to profitability is dependent upon the successful development, approval, and commercialization of its existing product candidates, including sapanisertib and mivavotinib, and the achievement of a level of revenues adequate to support its cost structure. In accordance with Accounting Standards Codification, or ASC, 205-40, Going Concern, the Company evaluated whether there are conditions and events, considered in the aggregate, that raise substantial doubt about its ability to continue as a going concern within one year after the date that these condensed consolidated financial statements are issued on August 15, 2022. This evaluation initially does not take into consideration the potential mitigating effect of management’s plans that have not been fully implemented as of the date the financial statements are issued. When substantial doubt exists under this methodology, management evaluates whether the mitigating effect of its plans sufficiently alleviates substantial doubt about the Company’s ability to continue as a going concern. The mitigating effect of management’s plans, however, is only considered if both (1) it is probable that the plans will be effectively implemented within one year after the date that the financial statements are issued, and (2) it is probable that the plans, when implemented, will mitigate the relevant conditions or events that raise substantial doubt about the entity’s ability to continue as a going concern within one year after the date that these condensed consolidated financial statements are issued. In performing its analysis, management excluded certain elements of its operating plan that cannot be considered probable. Under ASC 205-40, the future receipt of potential funding from future equity or debt issuances cannot be considered probable at this time because these plans are not entirely within the Company’s control and have not been approved by the board of directors as of the date of these condensed consolidated financial statements. The Company's expectation to generate operating losses and negative operating cash flows in the future and the need for additional funding to support its planned operations raise substantial doubt regarding the Company’s ability to continue as a going concern for a period of one year after the date that these condensed consolidated financial statements are issued on August 15, 2022. Management's plans to alleviate the conditions that raise substantial doubt include the pursuit of additional cash resources through sales of shares of its capital stock, reduced 2022 and 2023 spending, and potentially through strategic collaboration or licensing agreements. Management has concluded the likelihood that its plan to successfully obtain sufficient funding from one or more of these sources, or adequately reduce expenditures, while reasonably possible, is less than probable. Accordingly, the Company has concluded that substantial doubt exists about the Company’s ability to continue as a going concern for a period of at least 12 months from the date of issuance of these condensed consolidated financial statements. The accompanying financial statements have been prepared on a going concern basis, which contemplates the realization of assets and satisfaction of liabilities in the ordinary course of business. The financial statements do not include any adjustments relating to the recoverability and classification of recorded asset amounts or the amounts and classification of liabilities that might result from the outcome of the uncertainties described above. Certain Effects of the Reverse Stock Split The Company's stockholders approved a reverse stock split of the Company's common stock on June 1, 2022, which became effective on June 14, 2022, or the Reverse Stock Split. On that date, every 20 issued and outstanding shares of the Company's common stock automatically converted into one outstanding share of common stock. As a result of the Reverse Stock Split, the number of the outstanding shares of common stock decreased from 97,300,826 (pre-split) shares to 4,865,036 (post-split) shares. In addition, by reducing the number of outstanding shares, the Company's loss per share in all prior periods increased by a factor of 20. The Reverse Stock Split affected all shares of common stock outstanding immediately prior to the effective time of the Reverse Stock Split, as well as the number of shares of common stock available for issuance under the Company's equity incentive plans and employee stock purchase plan. In addition, the Reverse Stock Split effected a reduction in the number of shares of common stock issuable upon the conversion of shares of Series A convertible preferred stock, or the Series A preferred stock, and upon the exercise of the stock options and warrants outstanding immediately prior to the effectiveness of the Reverse Stock Split. The reverse stock split affected all holders of common stock uniformly, and did not affect any stockholder's percentage of ownership interest. The par value of the Company's common stock remained unchanged at $0.0001 per share and the number of authorized shares of common stock remained the same after the Reverse Stock Split. As the par value per share of the Company's common stock remained unchanged at $0.0001 per share, the change in the common stock recorded at par value has been reclassified to additional paid-in-capital on a retroactive basis. All references to shares of common stock and per share data for all periods presented in the accompanying financial statements and notes thereto have been adjusted to reflect the reverse stock split on a retroactive basis.

Organization and Basis of Presentation

6 Months Ended

Jun. 30, 2022

Organization, Consolidation and Presentation of Financial Statements [Abstract]

1. Organization and Basis of Presentation

Organization

Calithera Biosciences, Inc., or the Company, was incorporated in the State of Delaware on March 9, 2010. The Company is a fully-integrated, clinical stage precision oncology biopharmaceutical company. Driven by a commitment to rigorous science and a passion for improving the lives of people impacted by cancer, Calithera is advancing a pipeline of investigational, small molecule oncology compounds with a biomarker-driven approach. The Company’s principal operations are based in South San Francisco, California, and it operates in one segment.

Presentation

The condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries, Calithera Biosciences UK Limited and Calithera Biosciences Ireland Limited. All significant intercompany accounts and transactions have been eliminated from the condensed consolidated financial statements.

The Company's Ability to Continue as a Going Concern

As of June 30, 2022, the Company had cash and cash equivalents of $41.8 million. The Company has incurred losses since inception and to date has financed its operations primarily through the sale of shares of its capital stock and payments from the Company’s collaboration and licensing agreements. As of June 30, 2022, the Company had an accumulated deficit of $495.9 million. During the year ended December 31, 2021 and six months ended June 30, 2022, the Company incurred a loss from continuing operations of $115.1 million and $22.9 million, respectively, and used $66.3 million and $27.3 million of cash in operations, respectively. The Company expects to continue to generate operating losses and negative operating cash flows for the foreseeable future and will need additional funding to support its planned operating activities through profitability. The transition to profitability is dependent upon the successful development, approval, and commercialization of its existing product candidates, including sapanisertib and mivavotinib, and the achievement of a level of revenues adequate to support its cost structure.

In accordance with Accounting Standards Codification, or ASC, 205-40, Going Concern, the Company evaluated whether there are conditions and events, considered in the aggregate, that raise substantial doubt about its ability to continue as a going concern within one year after the date that these condensed consolidated financial statements are issued on August 15, 2022. This evaluation initially does not take into consideration the potential mitigating effect of management’s plans that have not been fully implemented as of the date the financial statements are issued. When substantial doubt exists under this methodology, management evaluates whether the mitigating effect of its plans sufficiently alleviates substantial doubt about the Company’s ability to continue as a going concern. The mitigating effect of management’s plans, however, is only considered if both (1) it is probable that the plans will be effectively implemented within one year after the date that the financial statements are issued, and (2) it is probable that the plans, when implemented, will mitigate the relevant conditions or events that raise substantial doubt about the entity’s ability to continue as a going concern within one year after the date that these condensed consolidated financial statements are issued. In performing its analysis, management excluded certain elements of its operating plan that cannot be considered probable. Under ASC 205-40, the future receipt of potential funding from future equity or debt issuances cannot be considered probable at this time because these plans are not entirely within the Company’s control and have not been approved by the board of directors as of the date of these condensed consolidated financial statements.

The Company's expectation to generate operating losses and negative operating cash flows in the future and the need for additional funding to support its planned operations raise substantial doubt regarding the Company’s ability to continue as a going concern for a period of one year after the date that these condensed consolidated financial statements are issued on August 15, 2022. Management's plans to alleviate the conditions that raise substantial doubt include the pursuit of additional cash resources through sales of shares of its capital stock, reduced 2022 and 2023 spending, and potentially through strategic collaboration or licensing agreements. Management has concluded the likelihood that its plan to successfully obtain sufficient funding from one or more of these sources, or adequately reduce expenditures, while reasonably possible, is less than probable. Accordingly, the Company has concluded that substantial doubt exists about the Company’s ability to continue as a going concern for a period of at least 12 months from the date of issuance of these condensed consolidated financial statements.

The accompanying financial statements have been prepared on a going concern basis, which contemplates the realization of assets and satisfaction of liabilities in the ordinary course of business. The financial statements do not include any adjustments relating

to the recoverability and classification of recorded asset amounts or the amounts and classification of liabilities that might result from the outcome of the uncertainties described above.

Certain Effects of the Reverse Stock Split

The Company's stockholders approved a reverse stock split of the Company's common stock on June 1, 2022, which became effective on June 14, 2022, or the Reverse Stock Split. On that date, every 20 issued and outstanding shares of the Company's common stock automatically converted into one outstanding share of common stock. As a result of the Reverse Stock Split, the number of the outstanding shares of common stock decreased from 97,300,826 (pre-split) shares to 4,865,036 (post-split) shares. In addition, by reducing the number of outstanding shares, the Company's loss per share in all prior periods increased by a factor of 20. The Reverse Stock Split affected all shares of common stock outstanding immediately prior to the effective time of the Reverse Stock Split, as well as the number of shares of common stock available for issuance under the Company's equity incentive plans and employee stock purchase plan. In addition, the Reverse Stock Split effected a reduction in the number of shares of common stock issuable upon the conversion of shares of Series A convertible preferred stock, or the Series A preferred stock, and upon the exercise of the stock options and warrants outstanding immediately prior to the effectiveness of the Reverse Stock Split. The reverse stock split affected all holders of common stock uniformly, and did not affect any stockholder's percentage of ownership interest. The par value of the Company's common stock remained unchanged at $0.0001 per share and the number of authorized shares of common stock remained the same after the Reverse Stock Split.

As the par value per share of the Company's common stock remained unchanged at $0.0001 per share, the change in the common stock recorded at par value has been reclassified to additional paid-in-capital on a retroactive basis. All references to shares of common stock and per share data for all periods presented in the accompanying financial statements and notes thereto have been adjusted to reflect the reverse stock split on a retroactive basis.