Colon & Rectal Cancer Screening & Diagnosis

Colon and rectal cancer screening and diagnosis at a glance

  • Regular colon and rectal cancer screenings, which are tests to detect pre-cancer or cancer before symptoms appear, can help oncologists prevent colon and rectal cancer or diagnose cancer at an early stage when treatment can be more effective.
  • Waiting until symptoms appear to look for colon and rectal cancer often means the cancer has already spread.
  • According to the American Cancer Society, colon and rectal cancer has a more than 90 percent survival rate if diagnosed early.
  • Colon and rectal cancer screening procedures include colonoscopy, CT scans, double-contrast barium enema and various stool tests.

Colon and rectal cancer screening and diagnosis

Colon and rectal cancer, together known as colorectal cancer, is the third leading cause of cancer deaths among men and women in the United States. Yet oncologists can readily diagnose and more effectively treat such cancer if it is discovered early through colon and rectal cancer screening and tests to detect the presence of cancer before symptoms appear. Oncologists can often cure colorectal cancer if treated in the beginning stages.

Finding and removing polyps early also helps prevent the formation of colorectal cancer. When individuals should seek colon and rectal cancer screenings depends on individual risk factors. According to the American Cancer Society (ACS), people at high risk should consider screening before age 50. These high risks include:

  • Personal or family history of colorectal cancer or polyps
  • Has had inflammatory bowel disease
  • Family history of inherited colorectal cancer syndromes such as familial adenomatous polyposis (FAP).

The ACS says all men and women over the age of 50 who are at average risk for developing colon cancer should receive one of the following screening tests, described in further detail below:

  • Colonoscopy, generally every 10 years
  • Flexible sigmoidoscopy every five years
  • Double-contrast barium enema every five years
  • CT colonography every five years
  • Guaiac-based fecal occult blood test annually
  • Fecal immunochemical test annually
  • Stool test for DNA every three years.

If any of the tests are positive for polyps or cancer, a colonoscopy test should be done.


A flexible sigmoidoscopy allows the doctor to examine the rectum and the lower colon. The oncologist inserts through the anus the flexible sigmoidoscope, a 60 cm long tube about the thickness of the pinky finger, into the rectum and colon.

This allows the doctor to diagnose colorectal cancer and determine probable causes of rectal bleeding, changes in bowel habits, pain and diarrhea.


A colonoscopy allows the doctor to examine the inner lining of the colon and rectum looking for polyps and abnormal growths that could become cancerous. The doctor inserts the colonoscope, a thin, flexible tube with a light and camera, into the colon through the anus.

Colonoscopes are typically between 48 and 72 inches in length so that they can view the entire colon, which is an average of six feet long.

During the colonoscopy the doctor can insert small instruments through the colonoscope to take tissue samples or remove polyps and other abnormal growths.

Double contrast barium enema

A double contrast barium enema is an X-ray examination of the colon and rectum. First, the oncologist will fill the colon with a contrast dye containing barium via a tube inserted into the anus. The barium dye blocks the X-rays and allows the colon to show up clearly on the X-ray.

The oncologist drains the barium dye from the colon, leaving a very thin layer of barium on the inner wall of the colon. The doctor will then fill the colon with air in order to achieve a more detailed view of the wall of the colon.

This view allows doctors to evaluate symptoms such as abdominal pain, blood in the stool or abnormal bowel movements and to diagnose inflammation, polyps and colorectal cancer.

CT colonography

A CT colonography, also known as a virtual colonoscopy, uses computed tomography technology to create images of the inside of the colon. A CT colonography can diagnose polyps or cancer in the colon and rectum.


A Guaiac-based fecal occult blood test (gFOBT) can be taken in the privacy of one’s home. The test uses guaiac, a chemical found in the wood resin of Guajacum trees, to determine if heme, the iron-containing component of hemoglobin, is present in the stool sample.

Polyps and cancer tissue are often very fragile and can be damaged by passing stool, causing microscopic amounts of blood to be released into the stool. Other causes of blood in the stool may be ulcers, hemorrhoids or colitis.

Fecal immunochemical test (FIT)

The fecal immunochemical test (FIT) is an at-home stool screening that detects small amounts of blood in stool caused by polyps and cancerous tissue that are damaged as the stool passes through the colon. Once the patient retrieves a stool sample, he or she sends it to a lab for testing.

Stool DNA test

A stool DNA test detects changes in the deoxyribonucleic acid (DNA) of the wall of the colon. During each bowel movement, both noncancerous and any present cancerous cells are shed into the stool. This test is designed for healthy people with no symptoms of polyps or colon cancer.

Colon and rectal cancer screening and diagnosis risks 

While colon and rectal cancer screenings such as colonoscopy may be uncomfortable, the risks and side effects are minimal. Typical risks and side effects include:

  • Abdominal cramping
  • Slight bleeding for several bowel movements after the exam
  • Infection.
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