Colorectal (colon) cancer is the third leading cause of death-after lung cancer and breast cancer-among women in the US. More than 70,000 women are diagnosed with colon cancer each year. Screening exams for colorectal cancer reduce mortality by detecting precancerous growths (polyps) and cancers at an early stage when they are most treatable. Research has shown that regular screening saves lives, yet an estimated 37 percent of the target population forgo screening.
"Many women have anxiety about colorectal cancer screenings. They fear that the advance prep will be miserable and that the test itself will be uncomfortable. Some women also underestimate their risk and assume that they can put off testing until a later time," said Cheryl B. Iglesia, MD, chair of The College's Committee on Gynecologic Practice. "But even though colon cancer is relatively slow-growing, time is of the essence and the sooner that abnormalities are detected, the better."
All women should be screened regularly for colon cancer beginning at age 50, or earlier for African American women and those at increased risk. Women at increased risk include those who have a first-degree relative younger than age 60 or two or more first-degree relatives of any age with colorectal cancer or polyps; had colorectal cancer or polyps themselves; had bowel disease, such as chronic ulcerative colitis, inflammatory bowel disease, or Crohn's disease; or a family history of certain types of colon problems or colon cancer.
"It's important that ob-gyns be familiar with the various forms of screening exams for colon cancer," Dr. Iglesia said. The new Committee Opinion reviews five common screening tests and two newer tests that are currently available for colon cancer screening along with the risks, benefits, and recommended frequency of each one. "No one screening method is best for every woman, so we must lay out the options, help them understand the benefits and drawbacks of each, and let them select the test that best suits them," Dr. Iglesia added.
According to the Committee Opinion, tests that detect both polyps and early colorectal cancer should be encouraged. However, all methods described in the document are suitable methods for cancer screening.
Tests that Detect Both Polyps and Cancer
The College recommends colonoscopy as the preferred method of colorectal cancer screening. Colonoscopy allows for the visualization of the whole colon, including the right side of the colon-an area where 65 percent of advanced cancers are found and that other screening exams can miss. The 20-30 minute exam is usually performed with the patient under sedation and is repeated infrequently (every 10 years).
Colonoscopy carries a higher risk of serious complications, such as perforation, hemorrhage, and severe abdominal pain, than other methods. Some women may find colonoscopy to be more inconvenient because it requires advanced bowel preparation, a missed day at work, and chaperoned transportation following the procedure because of sedation. But having a colonoscopy to start may save time in the long run. According to Dr. Iglesia, "positive test results from one of the other invasive or non-invasive exams almost always necessitate a follow-up diagnostic colonoscopy. You may wind up having two tests at the end of the day."
Flexible sigmoidoscopy uses a thin, flexible tube to examine the rectum and lower colon and to remove some polyps. The exam can also detect certain types of polyps found in the rectum that may signal a higher risk of cancer in other parts of the colon. Flexible sigmoidoscopy is limited to the lowest part of the colon and may miss a significant number of right-sided lesions, particularly in women and African Americans. Compared with colonoscopy, flexible sigmoidoscopy is technically easier, requires less bowel preparation, can be performed without sedation, and has a lower risk of complications. However, colonoscopy is usually required if test results come back positive. This screening is recommended every five years.
In a double contrast barium enema, the entire colon is stained using a contrast dye enema, and then x-rayed. The x-rays are examined for signs of polyps and cancer. This procedure requires a complete bowel prep and lacks the sensitivity of some other exams, but it carries a low-risk of complications, such as bowel perforation. If polyps of more than 6 mm are discovered, a follow-up colonoscopy will be recommended.
Virtual colonoscopy is an emerging, non-invasive imaging exam that is currently being evaluated as an additional option for colorectal cancer screening. Following a complete bowel preparation, computed tomography is used to detect polyps and cancerous lesions. This procedure can drastically reduce the risk of perforation, but if polyps are found, a standard colonoscopy is needed. Practitioners offering virtual colonoscopy should also consider offering same-day colonoscopy to avoid the need for a second bowel prep. Because this is a newer procedure, access to this test may be limited and radiologists experienced in evaluating these exams may not be widely available.
Tests that Detect Cancer Only
High-sensitivity guaiac fecal occult blood test (gFOBT) or fecal immunochemical test (FIT) are non-invasive tests that detect hidden blood in the stool caused by large polyps (greater than 1 cm) or cancer. For both tests, patients collect stool samples at home for several days. Samples are sent to a lab to be checked for hidden blood. Research suggests that gFOBT and FIT testing lead to detection of cancer at an early and more curable stage. These screenings must be performed annually. A follow-up colonoscopy will be recommended if the test comes back positive.
Fecal DNA testing is a newer screening exam that detects genetic mutations in the stool associated with colorectal cancer. A single, home-collected stool sample is required for this screening test. The test presents no direct risk to the colon, no bowel preparation is necessary, and there are no pretest dietary modifications. A recent study found fecal DNA testing to be more effective in detecting hidden blood than FOBT testing. This promising technique is still evolving and no test is widely used to date. Recommended frequency of fecal DNA testing is unspecified.
Committee Opinion #482, "Colonoscopy and Colorectal Cancer Screening Strategies," is published in the March 2011 issue of Obstetrics & Gynecology.
Source:
American College of Obstetricians and Gynecologists
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