Excluding skin cancer, colorectal cancer is the third most common type of cancer in both men and women the U.S. It strikes more than 140,000 Americans and kills about 50,000 every year. It's one of the most curable cancers if detected early, but it often produces no symptoms until it's beyond successful treatment. Researchers think that most colon cancers develop when environmental factors interact with a person’s inherited or acquired susceptibility. Most colon cancers come from a type of growth in the large intestine called an adenomatous polyp. These polyps can slowly change, usually taking many years to develop into cancer.

That's why everyone should be aware what risk group he or she falls into and when to begin screening for colorectal cancer.

All women and men at average risk for colorectal cancer should have a screening test for colorectal cancer beginning at age 50. Colorectal cancer is rarely found in people under the age of 50.

People who are at higher risk for colorectal cancer may need to begin screening tests at a younger age. People at higher risk include:

  • Those with familial polyposis. This is a family history of development of multiple polyps likely to become cancerous. Although only about 1 percent of all colorectal cancer patients have this gene, those who do have it have a nearly 100 percent chance of developing cancer. People with this cancer will likely die in their 40s if not treated. They should start screening in their teenage years.

  • Those with hereditary nonpolyposis cancer (HNPCC, also known and Lynch syndrome), which is brought about by defective DNA repair genes. About 3 to 5 percent of people with colon cancer have this condition. People with HNPCC typically have parents or siblings who developed colorectal cancer before age 50. They should start screening in their 20s, or about 10 years before the youngest age of the family member who developed colorectal cancer.

  • Those who have had colorectal cancer or a precancerous polyp.

  • Those who have a parent, sibling, or child who has had colorectal cancer before the age of 60, or if more than one relative is affected (at any age), have a two to four times greater risk.

  • Those who have chronic inflammatory bowel disease (ulcerative colitis or Crohn's colitis), a condition that causes the colon to be chronically inflamed, have an increased risk of developing colon cancer. Screening should be started at a young age and be done more frequently.

Several methods can be used for screening. A person’s preference and the recommendation of his or her health care provider should determine which test is used and how frequently a person is screened.

Screening tests

The fecal occult blood test (FOBT) and fecal immunochemical test (FIT) look for hidden (occult) blood in stool. Blood in the stool can be caused by a variety of conditions; colorectal cancer is only one of them. The FOBT uses a chemical reaction to detect blood in small samples of stool that have been placed on a FOBT sample card. Usually two samples from each of three consecutive stools are collected at home and mailed or taken to your health care provider’s office for testing. Certain foods or drugs can affect the FOBT, so you should follow instructions on diet and medications. The FIT looks for a specific part of a human blood protein. Collecting samples for the FIT is easier (there are no drug or dietary restrictions during testing), but the test is more expensive than the FOBT. The American Gastroenterological Association (AGA) and the American Cancer Society  (ACS) say that if a test is positive for blood in stool, a colonoscopy should be done to determine the source of the bleeding. It could be caused by cancer, a polyp, hemorrhoids, diverticulosis (a condition in which small pouches form at weak spots in the wall of the colon), or inflammatory bowel disease, also called colitis. If cancer or a precancerous polyp does not bleed, this test will not detect it. For people at average risk who choose this test, the ACS and the AGA recommend that it be done once a year.

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