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.