Summit Therapeutics Inc.

Item 8.01 Other Events. On July 22, 2026, Summit Therapeutics Inc. (the “Company”) issued a press release announcing results of an updated overall survival (“OS”) analysis from the Phase III HARMONi clinical trial (“HARMONi”). The HARMONi study is evaluating ivonescimab combined with chemotherapy compared to placebo plus chemotherapy in patients with endothelial growth factor receptor (“EGFR”)-mutated, locally advanced or metastatic non-squamous non-small cell lung cancer who were previously treated with a third-generation EGFR tyrosine kinase inhibitor. The updated analysis that was conducted with a data cutoff date of June 2026 analyzed OS when most western patients had discontinued treatment or completed two years of treatment. This analysis showed a consistent OS trend amongst western and Asian patients as western patients were followed for additional time on study reaching median follow-up of 23.2 months; Asian patients remained locked with a median follow-up time of 32.7 months from the primary analysis. A hazard ratio of 0.76 was observed for the full population; the 0.76 hazard ratio was also observed in western patient subgroups, respectively, in this analysis. Ivonescimab continued to demonstrate an acceptable and manageable safety profile, that was consistent with previous Phase III data of ivonescimab plus chemotherapy with no additional safety signals noted. These OS results have been made available to the FDA, and more detailed data are intended to be presented at an upcoming medical conference. A copy of the press release is attached as Exhibit 99.1 to this Current Report on Form 8-K and is incorporated by reference herein.