Colon cancer is a type of cancer that affects the large intestine, specifically the colon. It is one of the most common types of cancer, and it can be fatal if left untreated. Rectal cancer is a type of cancer that affects the rectum, the last part of the large intestine. It can also be fatal if left untreated, and it shares many of the same risk factors as colon cancer. Early detection and treatment are crucial for both types of cancer.