Colorectal cancer starts with polyps, or growths of the colon lining. Polyps known as adenomas are the precursors of colorectal cancer. The risk factors for adenoma and cancer development are not all identified. High fat, low fiber diets, increasing age and gene abnormalities are the best known risk factors.
The majority of people who develop colorectal cancer have no known risk factors. However, chronic inflammatory conditions of the colon (ulcerative colitis or Crohn’s disease), a family or personal history of colorectal cancer, adenomatous polyps or hereditary polyp syndromes are all associated with an increased risk.