Excluding skin cancer, colorectal cancer is the third most common type of cancer in both men and women in 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 adenomatous polyposis (FAP). This is a family history of development early in life 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 at 10 to 12 years of age.
Those with hereditary nonpolyposis cancer (HNPCC, also known as 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). These people have a two to four times greater risk. Screening should start at age 40, or 10 years before the age of the earliest colorectal cancer in the family.
Those who have chronic inflammatory bowel disease (ulcerative colitis or Crohn's colitis), a condition that causes the colon to be chronically inflamed. These people 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.
The fecal occult blood test (FOBT) and fecal immunochemical test (FIT). These tests 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.
Sigmoidoscopy. This test uses a short, flexible, lighted tube that is inserted into the rectum and gently moved into the lower part of the colon. It is less involved than a colonoscopy and has been shown to lower the risk of dying from colorectal cancer, but only covers the lower part of the colon, representing less than half the surface at risk for developing cancer. If a polyp is found, it may be removed, but you will need a colonoscopy to look at the rest of the colon. Before this test is done, the colon and rectum must be cleaned with an enema. The ACS recommends that people at average risk who choose this test have it done every five years, or as instructed by your health care provider.
Colonoscopy. This test uses a colonoscope, a slender, flexible lighted tube that is longer than the one used for a sigmoidoscopy. In a colonoscopy, the entire colon is examined. If a polyp is found, it can be removed during the colonoscopy. Before a colonoscopy, the entire colon must be cleaned with laxatives or enemas. A colonoscopy can be uncomfortable, so an intravenous medication is usually used to make you feel sleepy during the procedure. A colonoscopy takes about 30 minutes, longer if a polyp is removed. A colonoscopy is recommended every 10 years, or as instructed by your health care provider.
Double-contrast barium enema (DCBE). This is a type of X-ray test. Barium sulfate, a chalky liquid, and air are infused through the rectum to outline the inner part of the colon and rectum to look for abnormal areas on X-rays. If suspicious areas are seen on this test, a colonoscopy will be needed to explore them further. This test is recommended every five years, or as instructed by your health care provider.
Newer methods of screening for colorectal cancer may be recommended as screening options:
Virtual colonoscopy (also known as CT colonography). This is a three-dimensional CT scan of the colon. Some people prefer it to a standard colonoscopy because it is not as invasive, although it still requires that the entire colon be cleaned with laxatives or enemas beforehand. If polyps are seen in a virtual colonoscopy, a standard colonoscopy will need to be done to remove them. This test should be done every five years, or as instructed by your health care provider.
Stool DNA tests. These tests look for certain abnormal sections of genetic material from cancer or polyp cells in the stool. They are not invasive and don't require any special preparation, but they are expensive. An entire stool sample is collected at home and mailed to a lab for processing. People having this test will receive a kit with detailed instructions from their health care provider's office or clinic on how to collect the specimen. As with other stool tests, if the results are positive, a colonoscopy is needed to investigate further. Because this is a newer type of test, the best length of time to go between tests is not yet clear.
The ACS makes the following recommendations:
If you have had a precancerous polyp or colorectal cancer, you should follow the recommendations of your health care provider.
If you have a parent or sibling who had colorectal cancer before the age of 60, or two or more close relatives who had colorectal cancer at any age, you should have a colonoscopy beginning at age 40, or 10 years before the youngest case in the immediate family. Screening by colonoscopy should continue every five years, or as instructed by your health care provider, as long as the results do not show a precancerous polyp or cancer.
If you have a family history of familial adenomatous polyposis, you should be under the care of a specialist, and you generally should begin screenings at puberty.
If you have a family history of HNPCC, you should be under the care of a specialist, and you generally should begin screening in your early 20s, or 10 years before the youngest case in your immediate family.
If you have inflammatory bowel disease (chronic ulcerative colitis or Crohn's disease), you should be under the care of a specialist who can determine when screening should begin.