Diet A high-fat, low-fiber diet is implicated in the development of colorectal cancer. Approximately 75% of colorectal cancers are sporadic and develop in people with no specific risk factors. Squamous cell carcinomas may develop in the transition area from rectum to anal verge and are considered anal carcinomas. Most (15-20%) colorectal cancers develop in people with either a positive family history or a personal history of colorectal cancer or polyps. The incidence and epidemiology, etiology, pathogenesis, and screening recommendations are common to both colon cancer and rectal cancer. Anal cancer is a rare malignancy that starts in the anus — the opening at the end of the rectum. The decreased incidence of colorectal cancer in African individuals is attributed to their high-fiber, low–animal-fat diet. According to the American Cancer Society, treatment usually involves two or more of these treatment strategies.