Additional Study Information: The purpose of this research study is to test how safe RP-6306 is at different doses and schedules, test how well RP-6306 works to shrink cancer in the body, and evaluate if food affects the way RP-6306 moves through your body. This study will test the investigational drug, RP-6306, for the first time in humans. Investigational means that the study drug being tested has not been approved by the United States Food and Drug Administration (FDA). RP- 6306 is a PKMYT1 inhibitor (blocks the activity of the PKMYT1 protein) that is designed to stop certain cancer cells from growing. You are being asked to participate in this study because you have an advanced cancer with a specific genetic change that is predicted to be sensitive to the study drug. Cancers may include breast cancer, esophageal cancer, kidney cancer, lung cancer, ovarian cancer, pancreatic cancer, colon and rectal cancer, head and neck/oral cancers, and liver cancer.