Colon cancer refers to cancer that starts in your large intestines. When excluding skin cancer, colon cancer is the third most common cancer in both men and women in the United States. You can develop colon cancer at any age. However, most people diagnosed with colon cancer are over age 50. Your cancer may come from a noncancerous polyp, which is a growth that develops along the wall of your large intestines. Polyps are usually small and don’t cause symptoms.  Your colon cancer screenings focus on finding and removing polyps before they turn cancerous.