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. There are more rare types of colorectal cancer but most cases, > 95%, are adenocarcinomas. Colorectal adenocarcinomas begin in the cells that line the inside of the colon and the rectum.

The average person in the United States has a lifetime risk for colorectal cancer that is 4.8%. Men have a slightly higher risk than women. Most cases, >90%, are diagnosed after the age of 50. The average age of diagnosis is 72. Some hereditary cancer syndromes cause an increased risk for colorectal cancer.

General Risk Factors

  • Adenomatous colon polyps (a type of colon polyp that is likely to develop into colorectal cancer)
  • Inflammatory bowel 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

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, which can include 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, unexplained weight loss, a continued feeling of tiredness, 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.

Men and women at average risk for colorectal cancer are recommended to begin colorectal cancer screening at the age of 50. 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. The colonoscope can also be used to remove polyps (some of which could eventually become cancerous if left in the colon) and take additional tissue samples. 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). 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 50. 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.

Colorectal Cancer Screening Methods (ACS)
Screening Method Age to Begin Frequency
Flexible sigmoidoscopy 50 Every 5 years
Colonoscopy 50 Every 10 years
Double-contrast barium enema 50 Every 5 years
CT colonography (virtual colonoscopy) 50 Every 5 years
Fecal occult blood test 50 Annually
Fecal immunochemical test 50 Annually

Health care providers may recommend a specific screening method or modifications to ages to begin or frequency of screenings based on a patient’s medical history or family history of colorectal cancer.

Flexible sigmoidoscopy, colonoscopy, double-contrast barium enema, and CT colonography can detect colon polyps and cancer. Fecal occult blood and fecal immunochemical tests can primarily detect the presence of cancer.

If a colonoscopy is not a patient’s primary screening method, a colonoscopy may have 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. Learn more about colon cancer treatments here.

Avoid the following

General Population
Familial Risk
11% One affected first-degree relative
Hereditary Risk
7.2 - >99%