A Study to Investigate the Safety and Preliminary Efficacy of GSK5460025 Alone or in Combination With Other Anti-cancer Agents in Participants With Solid Tumors

This study is testing a new drug called GSK5460025, alone or in combination with other cancer treatments, for people with advanced solid tumors that have a specific feature called mismatch repair deficiency (dMMR) or microsatellite instability (MSI-H). These features mean the cancer has trouble repairing its own DNA. **You may be eligible if...** - You have advanced (unresectable or metastatic) solid tumor cancer — including colorectal or endometrial cancer - Your tumor has dMMR/MSI-H status, or this can be tested - You have tried all available standard treatments (for Part 1), or have received 1–3 prior treatments including at least one immunotherapy (for Part 2) - You are reasonably functional (ECOG 0–2) with at least 3 months life expectancy - Your organs are functioning adequately **You may NOT be eligible if...** - You have untreated or progressing brain metastases - You have not recovered from side effects of prior cancer treatments - You have previously received a Werner helicase inhibitor or similar experimental drug - You have significant liver disease, uncontrolled gastrointestinal problems, or difficulty swallowing pills Talk to your doctor to see if this trial is right for you.