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...