Virginia Commonwealth University

VCU Massey Cancer Center

What causes colorectal cancer?

The exact cause of colorectal cancer is unknown. Age and health history can affect the risk of developing colorectal cancer. Approximately 25 percent of individuals with colorectal cancer have at least one relative with colorectal cancer, while 75 percent of cases are persons without a family history.

Approximately 5 percent to 6 percent of colorectal cancers are due to known predisposing genetic factors. This means that the majority of colorectal cancers are, in fact, not inherited. Specifically, 3 percent to 5 percent of all colorectal cancer is due to hereditary nonpolyposis colon cancer, while approximately 1 percent is due to familial adenomatous polyposis.

Persons with a family history of colorectal cancer may wish to consider genetic testing. The American Cancer Society suggests that anyone undergoing such tests have access to a physician or geneticist qualified to explain the significance of the results.

 

What are the risk factors for colorectal cancer?

Risk factors may include:

  • Age – most people who have colorectal cancer are over age 50, however, it can occur at any age.
  • Polyps – benign growths on the wall of the colon or rectum are common in people over age 50, and are believed to lead to colorectal cancer.
  • Personal history – people who have had colorectal cancer, as well as ovarian, uterine or breast cancers, have a slightly increased risk for colorectal cancer.
  • Family history – people with a strong family history of colorectal cancer or adenomatous polyps in a first-degree relative (in a parent or sibling before the age of 60 or in two first-degree relatives of any age), have an increased risk for colorectal cancer.
  • Ulcerative colitis – people who have ulcerative colitis, an inflamed lining of the colon, have an increased risk for colorectal cancer.
  • Obesity.
  • Physical inactivity.
  • High-fat and/or low-fiber diet.
  • Alcohol consumption.
  • Smoking.