Cancer types Myrisk screens

Colon Cancer

The term colorectal cancer can be used to describe a cancer that begins in either the colon or the rectum. Cancer that begins in the colon is sometimes just called colon cancer, and cancer that begins in the rectum may just be called rectal cancer. The most common type of colorectal cancer is called adenocarcinoma. Colorectal adenocarcinomas begin in the cells that line the inside of the colon and the rectum.1,2,3

In the United States, the average person has a 4.2% lifetime risk for colon cancer, with men having a slightly higher risk than women.4 More than 93% of colorectal cancers occur after the age of 45.4 The median age of colon cancer diagnosis is 67, with men having a slightly higher risk for younger diagnoses than women.4 For reasons unknown, African Americans have the highest colorectal cancer incidence and mortality rates of all racial groups in the US.2 Some hereditary cancer syndromes cause an increased risk for colorectal cancer.1,2,3

General Risk Factors

  • Personal history of a previous colorectal cancer
  • Adenomatous colon polyps (a type of colon polyp that is likely to develop into colorectal cancer)
  • Inflammatory bowel disease, such as ulcerative colitis or Crohn’s disease
  • Type 2 diabetes (typically non-insulin dependent diabetes) – excess weight is also a risk factor for Type 2 diabetes, but studies that have taken this into account still suggest an increased colorectal cancer risk associated with Type 2 diabetes
  • Family history of cancer – having family members with colorectal cancer raises the risk of colorectal cancer, even in absence of a known hereditary cause
  • Diagnosis of a genetic colorectal cancer predisposition syndrome

As with the vast majority of cancers, there is no confirmed way to completely prevent the development of colorectal cancer. Eating a diet high in fruits and vegetables and low in red meat may help reduce the risk for colorectal cancer. Calcium and vitamin D supplements may also lower colorectal cancer risk. Nonsteroidal anti-inflammatory drugs (NSAIDs), like aspirin, have been suggested to reduce colon polyp development. Patients interested in using NSAIDs preventatively should discuss the benefits and risks with their health care provider. NSAID use cannot take the place of regular colorectal cancer screening, and routine use of NSAIDs can cause major side effects, such as stomach bleeding and stomach ulcers.

Symptoms of colorectal cancer can include a change in bowel habits, diarrhea, constipation, a feeling that the bowel does not completely empty, blood in the stool, narrowed or thinned stools, abdominal discomfort that can include gas pains, bloating, fullness, and cramps, vomiting, unexplained weight loss, a continued feeling of tiredness, and/or unexplained iron-deficiency anemia (low number of red blood cells.) These symptoms could also be due to common noncancerous conditions. Symptoms may be severe, long lasting, or change over time when associated with cancer.

There are numerous screening tests that can detect colorectal cancer. A test that can detect colorectal polyps in addition to detecting colorectal cancer if it is already present is colonoscopy. During a colonoscopy, a doctor inserts a colonoscope (a thin tube with a light and lens for viewing the inside of the colon) into the rectum and can view the entire length of the colon. Polyps can also be removed during colonoscopy, some of which could eventually become cancerous if left in the colon. A flexible sigmoidoscopy can also detect colorectal polyps and colorectal cancer, but during this test only a much shorter portion of the colon is evaluated in addition to the rectum. If an adenomatous polyp or colon cancer is identified during the test, a patient will likely need to undergo a colonoscopy for evaluation of the remaining colon. A double contrast barium enema and a virtual colonoscopy are imaging exams that can detect polyps and other suspicious areas in the colon and rectum, but polyps and tissue samples cannot be removed during these procedures. If any suspicious areas are identified, a patient will still need a colonoscopy. Fecal occult blood tests and fecal immunochemical tests are more likely to detect a colorectal cancer than polyps. Both of these tests are used to detect any hidden blood in the stool. Again, if any signs of cancer are noted on these tests, a patient will need a colonoscopy. The time between colorectal cancer screenings depends on a patient’s family history, the type of the screening test, and the result of the previous test (if screening has already begun.)

Men and women at average risk for colorectal cancer are recommended to begin colorectal cancer screening between ages 45-50.2,5,6 Specific guidelines from the American Cancer Society are detailed below.

Screening MethodAge to BeginFrequency
Colonoscopy45Every 10 years
CT colonography (virtual colonoscopy)45Every 5 years
Flexible sigmoidoscopy45Every 5 years
Fecal immunochemical test45Annually
Fecal occult blood test45Annually
Stool DNA test45Every 3 years

Patients who have a family history of colorectal cancer or who have a hereditary cancer syndrome associated with an increased risk for colorectal cancer may be told by their doctor that they need to begin colorectal cancer screening before age 45, and a specific screening method such as colonoscopy may be recommended. If cancer is identified or suspected based on results from any of the tests mentioned above, blood tests and additional imaging exams may be requested.

If a colonoscopy is not a patient’s primary screening method, a colonoscopy may still have to be performed to further investigate findings from another screening method.

If colorectal cancer is diagnosed following any of the tests above, treatment will depend on the stage of the cancer (how far the cancer has grown or spread). Treatment can include some combination of surgery, chemotherapy and radiation therapy.



  • A diet high in red meat and processed meats
  • A diet low in fruits and vegetables


  • Smoking


  • Being very overweight; having too much body fat

Lack of physical activity

  • Little exercise and a large amount of time spent sitting


  • Heavy alcohol use
General Population
Familial Risk
Varies between general population and hereditary risk based on family history and other factors
Hereditary Risk
Up to >99%


  1. American Society of Clinical Oncology: Colorectal Cancer (
  2. American Cancer Society: Colon Cancer (
  3. National Cancer Institute: Colon Cancer treatment (
  4. SEER Cancer Stat Facts: Colorectal Cancer. National Cancer Institute. Bethesda, MD,
  5. Provenzale D, et al. NCCN Clinical Practice Guidelines in Oncology®: Colorectal Cancer Screening. V1.2020. Available at
  6. Early Detection for Colorectal Cancer: ASCO Resource-Stratified Guideline. Journal of Global Oncology 2019; 5:1-22.
  7. Jasperson KW, et al. APC-Associated Polyposis Conditions. 2017 Feb 2. In: Pagon RA, et al., editors. GeneReviews® [Internet]. Available from