Early diagnosis of colorectal cancer depends on routine screening, which should typically begin at age 45 for people who are at average risk of developing colorectal cancer and continue until age 75. For adults aged 76 to 85, doctors take into consideration the person's overall health and the results of previous screenings and then decide whether to continue screening.
Screening begins earlier in some people. For example, people who have a first-degree relative (a parent, sibling, or child) who has had colorectal cancer before age 60 should begin screening every 5 years beginning at age 40 or 10 years earlier than the age of diagnosis of the relative, whichever is sooner. For example, if a person's father was diagnosed with colorectal cancer at age 45, he or she should begin screening at age 35.
Doctors do several different tests to screen for colorectal cancer:
People who have genetic causes of colorectal cancer, such as Lynch syndrome and MUTYH polyposis syndrome, need additional screenings.
Colonoscopy
Doctors often screen people using colonoscopy, in which the entire large intestine is examined. During colonoscopy, growths that appear cancerous (malignant) are removed using instruments passed through the scope. Growths are sent to the laboratory to be tested for cancer. Some larger growths must be removed during regular surgery.
Colonoscopy needs to be done every 10 years or more often in people at high risk of colorectal cancer.
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Stool Tests
Fecal immunochemical tests (FIT) are used to detect blood in the stool, even blood that cannot be seen by the naked eye (called occult blood). FIT are more accurate than older chemical-based stool tests and have no dietary restrictions. These tests are done every year. However, many disorders besides cancer can cause blood in the stool and not all cancers bleed at all times.
Fecal DNA tests are used to look in stool for genetic material from a cancer. Genetic stool tests are often combined with fecal immunochemical tests for blood (FIT-DNA tests) and are done at least every 3 years. People who have a positive FIT-DNA test should get a follow-up colonoscopy within 6 months to reduce the risk of missing an advanced colon cancer. About 10 to 15% of people who have a positive FIT-DNA test result have a normal colonoscopy. These people can have a repeat fecal FIT-DNA test in 1 year or a repeat colonoscopy in 3 years. If these results are negative, then people are considered to have an average risk of developing colon cancer and can return to the normal screening schedule.
Sigmoidoscopy
Sigmoidoscopy is an examination of the lower portion of the large intestine. This test is good for viewing growths in the sigmoid colon or rectum but does not allow doctors to see tumors further up in the colon.
Sigmoidoscopy needs to be done every 5 years or, if occult blood testing is also done, every 10 years.
Computed Tomography (CT) Colonography
CT colonography (virtual colonoscopy) generates two- and three-dimensional images of the colon by using a special CT scan technique. In this technique, people drink a contrast agent and their colon is inflated with gas from a tube inserted in the rectum. Viewing the high-resolution three-dimensional images somewhat simulates the appearance of regular colonoscopy, hence the name.
Virtual colonoscopy may be an option for people who are unable or unwilling to undergo the regular colonoscopy procedure, but it is less accurate and highly dependent on the skill and experience of the radiologist. This test does not require sedation but still requires a thorough bowel preparation, and the inflation of the colon with gas may be uncomfortable. Additionally, unlike with regular colonoscopy, lesions cannot be removed for examination under a microscope (biopsied) during the procedure. If a polyp or cancer is found during virtual colonoscopy, a regular colonoscopy is needed to remove the polyp or biopsy the cancer. Virtual colonoscopy can show whether cancer has spread outside of the colon to the lymph nodes or liver but is not good for detecting small polyps in the colon.
This test is done every 5 years.
Screening Tests for Genetic Causes of Colorectal Cancer
Lynch syndrome and MUTYH polyposis syndrome are disorders that are caused by mutations in certain genes. These mutations can cause colorectal cancer.
In addition to screening for colorectal cancer, people with Lynch syndrome require ongoing screening for other cancers. Such screening includes ultrasonography of the female organs (done through the vagina), examination of cells taken from the lining of the uterus (endometrium) with a suction device, and tests of the blood and urine.
First-degree relatives (a parent, sibling, or child) of people with Lynch syndrome who have not had genetic testing should have colonoscopy every 1 to 2 years beginning in their 20s and then every year after age 40. First-degree relatives who are women should be tested every year for endometrial and ovarian cancer.
People with MUTYH polyposis syndrome should have a colonoscopy every 1 to 2 years starting at age 25 to 30 (called surveillance colonoscopy). They also should be screened for tumors of the stomach and duodenum, thyroid, bladder, ovaries, and skin.
