Colon cancer, also known as colorectal cancer when it affects the rectum, begins in the large intestine (colon) or rectum. This type of cancer often starts as small, benign clumps of cells called polyps, which can develop into cancer over time. Symptoms can include changes in bowel habits, blood in the stool, abdominal discomfort, and unexplained weight loss. Regular screening, such as colonoscopy, is key to early detection and prevention.