Testing for Safety and Colorectal Cancer Preventive Effects of ONC201

This study is testing whether a drug called ONC201 can prevent colorectal polyps (pre-cancerous growths) from coming back or growing in people who are at high risk for colorectal cancer. This includes people with a hereditary condition called familial adenomatous polyposis (FAP) or those who have had many polyps found on a recent colonoscopy. **You may be eligible if...** - You are 18 or older at high risk for colorectal cancer (either due to FAP or a history of 5 or more small polyps, or 3 or more polyps with at least one large one) - You are due for a routine colonoscopy and have at least two polyps of 5 mm or larger that the doctor can mark and monitor - Your blood counts, liver, and kidney function are within acceptable ranges - Your expected survival is at least 5 years - You are willing to have a second follow-up endoscopy about 12 weeks after starting treatment **You may NOT be eligible if...** - You are pregnant or may become pregnant during the study (contraception is required) - You have had a prior unrelated invasive cancer in the past 5 years (minor exceptions apply) - Your overall health or organ function is significantly compromised Talk to your doctor to see if this trial is right for you.