The colon and rectum are part of the large intestine. Colorectal cancer occurs when tumors form in the lining of the large intestine. It is common in both men and women. Colon cancer is the third most common cause of cancer deaths in women and second most common in men in the United Stares. The risk of developing colorectal cancer rises after age 50. You're also more likely to get it if you have colorectal polyps, a family history of colorectal cancer, ulcerative colitis or Crohn's disease, eat a diet high in fat, or smoke.