Nature of Business and Basis of Presentation	6 Months Ended
Jun. 30, 2025
Disclosure Text Block [Abstract]
Nature of Business and Basis of Presentation	Note 1. Nature of Business and Basis of Presentation Description of business iTeos Therapeutics, Inc. ("iTeos Inc." or the "Company"), a Delaware corporation headquartered in Watertown, Massachusetts (incorporated on October 4, 2019), is the successor to iTeos Belgium SA (iTeos Belgium) a company organized under the laws of Belgium in 2011 and headquartered in Charleroi, Belgium. The Company has historically focused on pioneering the discovery and development of a new generation of immuno-oncology therapeutics for people living with cancer. The Company historically designed novel product candidates with optimized pharmacologic properties to improve clinical outcomes by restoring the immune response against cancer. The Company previously focused on advancing its innovative pipeline which includes monoclonal antibodies (mAbs) and small molecules for the treatment of cancer, especially solid tumors. Its immuno-oncology programs target three different key cancer resistance mechanisms: the TIGIT/CD226 pathway, which the Company targets with an antibody to TIGIT (T cell immunoreceptor with lg and ITIM domains); the adenosine pathway, where the Company uses a small molecule to inhibit ENT1 (equilibrative nucleoside transporter 1); and the reprogramming of immunosuppressive macrophages, where the Company antagonizes Triggering Receptor Expressed on Myeloid Cells 2 ("TREM2"), a critical receptor key to driving the tumor promoting functions of tumor resident macrophages. On December 2, 2020, iTeos Securities Corporation (iTeos SC) was incorporated as a Massachusetts Security Corporation. It is a wholly owned subsidiary of iTeos Inc. On July 27, 2021, iTeos BE, LLC (iTeos LLC) was incorporated as a Delaware Limited Liability Company. It is a wholly owned subsidiary of iTeos Inc. The Company’s lead clinical-stage antibody product candidate, belrestotug, also known as EOS-448/GSK4428859A, was an antagonist of TIGIT, an immune checkpoint with multiple mechanisms of action. On June 11, 2021, the Company's wholly owned subsidiary, iTeos Belgium, and GlaxoSmithKline Intellectual Property (No. 4) Limited ("GSK"), executed a Collaboration and License Agreement (the "GSK Collaboration Agreement"), which became effective on July 26, 2021. Pursuant to the GSK Collaboration Agreement, the Company granted GSK a license under certain of its intellectual property rights to develop, manufacture, and commercialize products comprised of or containing belrestotug, which license is exclusive in all countries outside of the United States and co-exclusive, with iTeos, in the United States. GSK and iTeos intended to develop belrestotug in combination, including with other oncology assets of GSK, and iTeos and GSK would jointly own the intellectual property created under the GSK Collaboration Agreement that covers such combinations. In partnership with GSK, the Company had multiple clinical trials: • GALAXIES Lung-301: global randomized, double blind Phase 3 registrational study assessing the doublet of GSK's anti-PD-1 (Jemperli (dostarlimab-gxly)) with belrestotug versus placebo and pembrolizumab in patients with first-line PD-L1 high non-small cell lung cancer ("NSCLC"). • GALAXIES Lung-201: global randomized, open label Phase 2 platform study assessing dostarlimab with belrestotug and in combination with GSK'608, GSK's investigational anti-CD96 antibody, nelistotug. • GALAXIES H&N-202: global randomized, open label Phase 2 study assessing dostarlimab with belrestotug and other novel immuno-oncology combinations, including nelistotug, in patients with first-line PD-L1 positive advanced metastatic head and neck squamous cell carcinoma ("HNSCC"). • TIG-006 HNSCC: open label Phase 1/2 study assessing dostarlimab with belrestotug in first-line PD-L1 positive advanced metastatic HNSCC. In May 2024, the Company announced completion of enrollment in the first portion of the Phase 2 expansion part of the trial. The Company and GSK agreed to not continue beyond stage 1 recruitment in these open-label cohorts in order to focus on the randomized, controlled GALAXIES H&N-202 platform study. On May 13, 2025, the Company reported topline results from an updated interim analysis of GALAXIES Lung-201. The Company reported that the GALAXIES Lung-201 data continued to demonstrate clinically meaningful improvements in the trial’s primary endpoint of objective response rate (“ORR”), but the analysis did not meet established criteria for clinically meaningful improvements in the secondary endpoint of progression free survival in the belrestotug + dostarlimab combination cohorts versus dostarlimab monotherapy. Additionally, an interim analysis of the GALAXIES H&N-202 Phase 2 trial showed a trend below the meaningful threshold for ORR in the belrestotug combination cohorts versus dostarlimab monotherapy in PD-L1 positive head and neck squamous cell carcinoma. Based on the results described above, the Company and GSK made the decision to terminate the belrestotug development program and end the collaboration, ending all belrestotug-containing cohorts and any new enrollment in the GALAXIES Lung-201 trial. On May 13, 2025, iTeos Belgium received written notice from GSK electing to terminate the GSK Collaboration Agreement. The Company's next most advanced program was EOS-984, a potentially first-in-class small molecule focused on a new mechanism in the adenosine pathway by targeting ENT1, a dominant transporter of extracellular adenosine, expressed on intratumoral T cells, which allows adenosine entry into the cell, disturbing T cell metabolism, expansion, effector function, and survival. The Company was evaluating EOS-984 in a Phase 1 Trial in advanced malignancies. The Company's most recent program to initiate a clinical trial was EOS-215, a potential best-in-class monoclonal antibody which antagonizes TREM2. Macrophages expressing TREM2 in tumors promote tumor growth and survival. The antibody is designed to block ligand binding and alter tumor resident macrophage function resulting in anti-tumor effects. EOS-215 has been shown preclinically to have a meaningful impact on macrophage function, promoting multiple anti-tumor mechanisms including T cell activation. The therapeutic candidate's multiple mechanisms of action have been shown to translate to activity in highly immune resistant models. s. On May 28, 2025, the Company announced its intention to wind down its clinical and operational activities. The action was taken as part of the Company’s review of strategic alternatives to maximize shareholder value following the Company’s decision to terminate its belrestotug development program and the termination of the Company’s collaboration with GSK (see Note 5). The Company is currently in the process of winding down its clinical activities. Liquidity and capital resources Since inception, the Company’s activities have consisted primarily of performing research and development to advance its product candidates. The Company had a net loss of $113.3 million and $45.3 million for the six months ended June 30, 2025 and 2024, respectively. As of June 30, 2025, the Company had an accumulated deficit of $123.1 million. On May 28, 2025, the Company announced, as part of a review of strategic alternatives aimed at maximizing shareholder value, its intention to wind down clinical and operational activities and that it expected such wind down to be substantially complete in the third quarter of 2025. Consequently, as of August 6, 2025, the issuance date of the condensed consolidated financial statements for the period ended June 30, 2025, the Company does not have an operational plan of business continuity. Therefore, there is substantial doubt about the Company's ability to continue as a going concern for at least 12 months from the issuance date of the condensed consolidated financial statements. In the event that the Merger is not consummated and the Company is unable to realize a strategic alternative and until such time as the Company is fully wound down, the Company expects to incur additional losses. Failure to manage discretionary spending or execute on a strategic alternative, including the Merger, will adversely impact the Company’s ability to achieve its intended business objectives. If the Company does not successfully consummate the Merger or other strategic transaction, the Board of Directors may decide to pursue a dissolution and liquidation of the Company. Basis of presentation The accompanying condensed consolidated financial statements and accompanying notes have been prepared in accordance with generally accepted accounting principles in the United States of America ("U.S. GAAP"). The unaudited interim condensed consolidated financial statements of the Company included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission ("SEC"). Certain information and footnote disclosures normally included in financial statements prepared in accordance with U.S. GAAP have been condensed or omitted from this report, as is permitted by such rules and regulations. Accordingly, these condensed consolidated financial statements should be read in conjunction with the consolidated financial statements as of and for the years ended December 31, 2024 and 2023, and the notes thereto, which are included in the Company’s Annual Report on Form 10-K (File No. 001-39401). The results for any interim period are not necessarily indicative of results for any future period. In the opinion of management, the information furnished reflects all adjustments, all of which are of a normal and recurring nature, necessary for a fair presentation of the results for the reported interim periods. The Company considers events or transactions that occur after the balance sheet date but before the financial statements are issued to provide additional evidence relative to certain estimates or to identify matters that require additional disclosure. The results of operations for interim periods are not necessarily indicative of results to be expected for the full year or any other interim period.

iTeos Therapeutics, Inc. ("iTeos Inc." or the "Company"), a Delaware corporation headquartered in Watertown, Massachusetts (incorporated on October 4, 2019), is the successor to iTeos Belgium SA (iTeos Belgium) a company organized under the laws of Belgium in 2011 and headquartered in Charleroi, Belgium. The Company has historically focused on pioneering the discovery and development of a new generation of immuno-oncology therapeutics for people living with cancer. The Company historically designed novel product candidates with optimized pharmacologic properties to improve clinical outcomes by restoring the immune response against cancer. The Company previously focused on advancing its innovative pipeline which includes monoclonal antibodies (mAbs) and small molecules for the treatment of cancer, especially solid tumors. Its immuno-oncology programs target three different key cancer resistance mechanisms: the TIGIT/CD226 pathway, which the Company targets with an antibody to TIGIT (T cell immunoreceptor with lg and ITIM domains); the adenosine pathway, where the Company uses a small molecule to inhibit ENT1 (equilibrative nucleoside transporter 1); and the reprogramming of immunosuppressive macrophages, where the Company antagonizes Triggering Receptor Expressed on Myeloid Cells 2 ("TREM2"), a critical receptor key to driving the tumor promoting functions of tumor resident macrophages.

On December 2, 2020, iTeos Securities Corporation (iTeos SC) was incorporated as a Massachusetts Security Corporation. It is a wholly owned subsidiary of iTeos Inc. On July 27, 2021, iTeos BE, LLC (iTeos LLC) was incorporated as a Delaware Limited Liability Company. It is a wholly owned subsidiary of iTeos Inc.

The Company’s lead clinical-stage antibody product candidate, belrestotug, also known as EOS-448/GSK4428859A, was an antagonist of TIGIT, an immune checkpoint with multiple mechanisms of action.

On June 11, 2021, the Company's wholly owned subsidiary, iTeos Belgium, and GlaxoSmithKline Intellectual Property (No. 4) Limited ("GSK"), executed a Collaboration and License Agreement (the "GSK Collaboration Agreement"), which became effective on July 26, 2021. Pursuant to the GSK Collaboration Agreement, the Company granted GSK a license under certain of its intellectual property rights to develop, manufacture, and commercialize products comprised of or containing belrestotug, which license is exclusive in all countries outside of the United States and co-exclusive, with iTeos, in the United States. GSK and iTeos intended to develop belrestotug in combination, including with other oncology assets of GSK, and iTeos and GSK would jointly own the intellectual property created under the GSK Collaboration Agreement that covers such combinations.

On May 13, 2025, the Company reported topline results from an updated interim analysis of GALAXIES Lung-201. The Company reported that the GALAXIES Lung-201 data continued to demonstrate clinically meaningful improvements in the trial’s primary endpoint of objective response rate (“ORR”), but the analysis did not meet established criteria for clinically meaningful improvements in the secondary endpoint of progression free survival in the belrestotug + dostarlimab combination cohorts versus dostarlimab monotherapy. Additionally, an interim analysis of the GALAXIES H&N-202

Phase 2 trial showed a trend below the meaningful threshold for ORR in the belrestotug combination cohorts versus dostarlimab monotherapy in PD-L1 positive head and neck squamous cell carcinoma.

Based on the results described above, the Company and GSK made the decision to terminate the belrestotug development program and end the collaboration, ending all belrestotug-containing cohorts and any new enrollment in the GALAXIES Lung-201 trial. On May 13, 2025, iTeos Belgium received written notice from GSK electing to terminate the GSK Collaboration Agreement.

The Company's next most advanced program was EOS-984, a potentially first-in-class small molecule focused on a new mechanism in the adenosine pathway by targeting ENT1, a dominant transporter of extracellular adenosine, expressed on intratumoral T cells, which allows adenosine entry into the cell, disturbing T cell metabolism, expansion, effector function, and survival. The Company was evaluating EOS-984 in a Phase 1 Trial in advanced malignancies.

The Company's most recent program to initiate a clinical trial was EOS-215, a potential best-in-class monoclonal antibody which antagonizes TREM2. Macrophages expressing TREM2 in tumors promote tumor growth and survival. The antibody is designed to block ligand binding and alter tumor resident macrophage function resulting in anti-tumor effects. EOS-215 has been shown preclinically to have a meaningful impact on macrophage function, promoting multiple anti-tumor mechanisms including T cell activation. The therapeutic candidate's multiple mechanisms of action have been shown to translate to activity in highly immune resistant models. s.

On May 28, 2025, the Company announced its intention to wind down its clinical and operational activities. The action was taken as part of the Company’s review of strategic alternatives to maximize shareholder value following the Company’s decision to terminate its belrestotug development program and the termination of the Company’s collaboration with GSK (see Note 5). The Company is currently in the process of winding down its clinical activities.

Since inception, the Company’s activities have consisted primarily of performing research and development to advance its product candidates. The Company had a net loss of $113.3 million and $45.3 million for the six months ended June 30, 2025 and 2024, respectively. As of June 30, 2025, the Company had an accumulated deficit of $123.1 million. On May 28, 2025, the Company announced, as part of a review of strategic alternatives aimed at maximizing shareholder value, its intention to wind down clinical and operational activities and that it expected such wind down to be substantially complete in the third quarter of 2025. Consequently, as of August 6, 2025, the issuance date of the condensed consolidated financial statements for the period ended June 30, 2025, the Company does not have an operational plan of business continuity. Therefore, there is substantial doubt about the Company's ability to continue as a going concern for at least 12 months from the issuance date of the condensed consolidated financial statements.

In the event that the Merger is not consummated and the Company is unable to realize a strategic alternative and until such time as the Company is fully wound down, the Company expects to incur additional losses. Failure to manage discretionary spending or execute on a strategic alternative, including the Merger, will adversely impact the Company’s ability to achieve its intended business objectives. If the Company does not successfully consummate the Merger or other strategic transaction, the Board of Directors may decide to pursue a dissolution and liquidation of the Company.

Basis of presentation

The accompanying condensed consolidated financial statements and accompanying notes have been prepared in accordance with generally accepted accounting principles in the United States of America ("U.S. GAAP").

The unaudited interim condensed consolidated financial statements of the Company included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission ("SEC"). Certain information and footnote disclosures normally included in financial statements prepared in accordance with U.S. GAAP have been condensed or omitted from this report, as is permitted by such rules and regulations. Accordingly, these condensed consolidated financial statements should be read in conjunction with the consolidated financial statements as of and for the years ended December 31, 2024 and 2023, and the notes thereto, which are included in the Company’s Annual Report on Form 10-K (File No. 001-39401). The results for any interim period are not necessarily indicative of results for any future period.

In the opinion of management, the information furnished reflects all adjustments, all of which are of a normal and recurring nature, necessary for a fair presentation of the results for the reported interim periods. The Company considers events or transactions that occur after the balance sheet date but before the financial statements are issued to provide additional evidence relative to certain estimates or to identify matters that require additional disclosure. The results of

operations for interim periods are not necessarily indicative of results to be expected for the full year or any other interim period.