Additional Study Information: The study is being done to learn how safe and effective the study drug, RP-3500, is when given with either niraparib or olaparib to treat advanced cancer. Niraparib and olaparib belong to a group of drugs called PARP inhibitors. These drugs are designed to block an enzyme called PARP which may stop cancer cells from growing. RP 3500 belongs to a class of drugs called ATR inhibitors that are designed to stop cancer cells from growing. Cancers include: bladder cancer, brain and spinal tumors, breast cancer, colon and rectal cancer, esophageal cancer, head and neck/oral cancers, liver cancer, lung cancer, melanoma, pancreatic cancer, prostate cancer, and stomach cancer.