This study looks at a medicine called navtemadlin to see if it helps patients with advanced or recurring endometrial cancer (a type of cancer that starts in the lining of the uterus) who have responded well to chemotherapy. The study has two parts. In the first part, different doses of navtemadlin will be tested for safety and effectiveness to find the best dose for the next phase. In the second part, the best dose will be compared to a placebo (a pill with no medicine in it) to see how well it works.

To join, patients must not have other types of cancer like sarcomas or certain small-cell cancers. They should not have had recent immune or experimental treatments, and must be in good health with good blood, liver, and kidney function. Some patients may not qualify if they have certain heart issues, surgical drains, or a history of bleeding problems.

• Study involves two parts: testing doses and comparing with placebo.
• Participants must have already responded to chemotherapy.
• No recent experimental treatments or certain health issues allowed.