Material Event (Form 8-K)

Clinical Collaboration with Roche in MTAP-Deleted RAS-Mutant Pancreatic Cancer

On June 3, 2026, IDEAYA Biosciences, Inc. (the "Company") announced it has entered into a clinical collaboration with F. Hoffmann-La Roche Ltd ("Roche") to evaluate the efficacy and safety of IDE892, its investigational, potential best-in-class PRMT5 inhibitor, in combination with Roche's RG6505, a pan-RAS inhibitor, in patients with pancreatic ductal adenocarcinoma ("PDAC") that carry an MTAP deletion. The Company will sponsor the clinical trial combination study, and Roche will supply RG6505.

IDE892 was designed to be a potential best-in-class PRMT5 inhibitor and has demonstrated robust monotherapy regressions in MTAP-deleted preclinical models. The Company is evaluating IDE892 in a Phase 1 dose escalation clinical trial in MTAP-deleted solid tumors and plans to initiate Phase 1 combination cohorts, in PDAC with RG6505 as well as in NSCLC and other solid tumors with IDE397, the Company's proprietary MAT2A inhibitor.

MTAP deletion is estimated to occur in up to 40% of PDAC and almost all MTAP-deleted PDAC harbor co-occurring RAS mutations. Combining a PRMT5 inhibitor with a pan-RAS inhibitor may have the potential to drive deeper and more durable responses for MTAP-deleted PDAC patients who currently have no approved targeted treatment options.

Under the clinical collaboration, the Company and Roche each retain all commercial rights to their respective compounds, including as monotherapy and as combination therapies. There will be a joint governance process between the Company and Roche to oversee the clinical combination study. The clinical collaboration also has the ability to evaluate a combination triplet with IDE892, RG6505, and IDE397, the Company's Phase 2 MAT2A inhibitor, upon joint approval from both the Company and Roche.