Additional Study Information: The purpose of this study is to test a new drug called RMC-6291, to evaluate its safety at different doses, and to find out how the body processes it. RMC-6291 is a new experimental drug, which means that it is not approved by the US Food and Drug Administration (FDA) or any other health authorities. This is the first study in which RMC-6291 will be tested in humans. Cancers include: bladder cancer, breast cancer, colon and rectal cancer, esophageal cancer, ovarian cancer, head and neck/oral cancer, kidney cancer, liver cancer, lung cancer, pancreatic cancer, prostate cancer, stomach cancer, testicular cancer, and thyroid cancer.