What is the risk of colorectal cancer?
Colorectal cancer is the second most common cancer in the United States. The average person's lifetime risk of developing it is about 1 in 20. It causes over 56,000 deaths annually. The risk is increased if there is a family history of colorectal polyps (pre-cancerous growths) or cancer. It is still higher for those with a personal history of polyps or colorectal, breast, uterine or ovarian cancer. Risk is also increased in people with a history of inflammatory bowel disease, such as ulcerative or Crohn's colitis.
What are screening and surveillance?
Screening is testing to identify whether a person with no symptoms has colon or rectal cancer or a disease or condition that may lead to such cancer. The goal is to identify pre-cancerous changes or early cancers when they are easier to prevent or cure. Surveillance is similar testing for people who have previously had colorectal cancer or pre-cancerous conditions. Because their chances of having cancer are higher, more frequent or extensive tests may be recommended.
Why should people be tested?
Colorectal cancer is known as a "silent" disease because in early stages, it rarely causes symptoms. Once symptoms such as bleeding, change in bowel function, and abdominal pain occur, the cancer may be difficult to cure. The possibility of curing patients after symptoms develop is only about 50%. Precancerous polyps can be cured 100% of the time and early cancers up to 90%. Treatment of polyps usually doesn't even require major surgery.
When and how often should testing be done?
For people who have none of the increased risks described above, screening should start at age 50. Colonoscopy every 10 years is preferred. Alternatives include annual stool testing and/or flexible sigmoidoscopy every 5 years. If stool testing is done, 3 stools should be tested each year. Stool should not be tested during a rectal examination. Barium enema every 5 years is the least preferred option.
People with a close relative, such as a sibling, parent or child who has had colorectal cancer or a polyp should have the same screening as above, but should start at age 40, or 10 years younger than the youngest age at which a relative was diagnosed.
People with a family history of colorectal cancer and/or certain related (urinary tract and gynecologic) cancers in several close relatives, especially cancers occurring at a young age, should receive genetic counseling and consider genetic testing for a condition called hereditary nonpolyposis colorectal cancer (HNPCC). People with this history should have colonoscopies every 1-2 years, beginning at age 20-25.
People with a family history of an inherited disease called familial adenomatous polyposis (FAP) should receive counseling and consider genetic testing to see if they have the gene that causes the disease. People who have the gene, whose tests are inconclusive, or who are not tested, should have a flexible sigmoidoscopy annually, starting at puberty. People whose gene testing is negative can be screened like people of average risk.
Women with a personal history of ovarian or uterine cancer before age 60 should undergo colonoscopy every 5 years starting at age 40, or the age of diagnosis, if that is later.
What screening tests are there?
Fecal occult blood testing uses chemical testing of stool samples to detect tiny, invisible amounts of blood. This test is inexpensive and simple but it only detects cancers or polyps that are bleeding at the time of the test. Only 50% of cancers and 10% of polyps bleed enough to be detected and even these only bleed some of the time. There are also times when the test shows blood but there are no polyps or cancers. If this test is positive, a colonoscopy (described later) is needed.
Flexible rectosigmoidoscopy is a test which allows a physician to look directly at the lining of the colon and rectum. A long, thin tube with an optical fiber or video chip is inserted through the anus and driven up the colon. This test is performed awake, in the doctor's office. The lining of the lower on-third of the colon can usually be seen. This part of the large intestine contains more than half of all polyps and cancers. If a polyp or cancer is found, colonoscopy is needed to examine the rest of the colon.
Colonoscopy is similar to sigmoidoscopy but the lining of the entire length of the colon is examined and the test is done with sedation. It is the test which is least likely to miss a polyp, cancer or other disease. Most colono-scopies are done on an outpatient basis with minimal inconvenience and discomfort.
Virtual colonoscopy uses CAT scans done while the colon is filled with air. Computer programs combine the CAT scan pictures into a "whole colon" image. This test has potential but the data on its accuracy is not yet sufficient to recommend for its use in screening. Like barium enema, it is sometimes used to look at the part of the colon which can't be reached during an incomplete colonoscopy.
People who have had a pre-cancerous polyp(s) found and removed should have a colonoscopy 3-5 years after the first examination, depending on the type and size of the polyp(s). Those with many or very advanced polyps may need a colonoscopy sooner and may need genetic counseling. If a polyp is incompletely removed, another colonoscopy will be needed in 3-6 months.
People with a personal history of colorectal cancer should have a colonoscopy within one year of removal of the cancer. If the whole colon was not examined before the cancer removal, they should have a colonoscopy in 3-6 months. If this is normal, they should have a follow-up exam in 2-3 years.
People with a history of extensive colitis (Crohn's or ulcerative) for 8 or more years should have colonoscopies with numerous biopsies every 1-2 years.