Approximately one in 20 adults will develop colorectal cancer in his or her lifetime. In the United States in 2004, an estimated 57,000 persons died from the disease. Recommended methods of screening for colorectal cancer include fecal occult blood testing, flexible sigmoidoscopy, air-contrast barium enema, and colonoscopy. Authorities recommend that asymptomatic, average-risk persons undergo some form of periodic screening starting at 50 years of age. Screening before then may be justified in individuals at higher risk, such as those with a first-degree relative affected by colorectal cancer or persons with hereditary cancer syndromes. Eisen and Weinberg reviewed screening recommendations for patients with family histories of colorectal cancer and outlined recent developments in screening technologies.
If a first-degree relative has a history of colorectal cancer or adenomatous polyps, a thorough family medical history should be collected. Information should include the affected relative’s age at diagnosis, location and number of lesions, medical histories of second-degree and more distant relatives, and a history of other family cancers that could suggest a hereditary nonpolyposis colon cancer (HNPCC). HNPCC results from mutations in DNA mismatch repair genes and causes 80 percent of affected patients to develop colorectal cancer by 50 years of age. Although HNPCC increases the risk of many different types of cancers, familial adenomatous polyposis (FAP) is a condition isolated to the colon. Characterized by the development of diffuse colonic polyps, FAP leads to colorectal cancer in nearly 100 percent of affected patients by 40 years of age. Physicians who suspect HNPCC or FAP from a family history should consider referring these patients for specialized genetic testing and counseling.
Although no prospective studies exist, expert consensus recommends beginning colorectal cancer screening at 40 years of age in patients with affected first-degree relatives, or 10 years before the relative’s age at diagnosis if the relative was younger than 40 years. Although multiple screening options are available to average-risk patients, it is recommended that patients with immediate family histories of colorectal cancer undergo colonoscopy at five-year intervals. If the patient declines colonoscopy, or if it is unavailable, air-contrast barium enema is recommended because it permits evaluation of the entire colon. The addition of flexible sigmoidoscopy also may be considered.
New screening technologies such as computed tomographic (CT) colonography and fecal DNA testing have demonstrated promise, but further testing is needed before they can be fully endorsed. CT colonography is limited by its low sensitivity for smaller polyps, requirement for cathartic bowel preparation, and need for subsequent conventional colonoscopy to verify and remove observed lesions. Although fecal DNA testing identified four times as many colonoscopy-verified cancers as fecal occult blood testing in a recent multicenter trial, it still missed 48 percent of clinically important lesions.
The authors conclude by reviewing the state of the evidence supporting dietary and chemopreventive interventions to reduce the future risk of colorectal cancer. Long-term calcium and folate supplementation appears to modestly reduce colorectal cancer rates in epidemiologic observational studies, whereas vitamin A, C, and E supplementation showed no benefit. Low-dose aspirin and the cyclooxygenase-2 inhibitor celecoxib (Celebrex) may have a small protective effect against the development of adenomas. Both are known to produce undesirable side effects, such as gastrointestinal bleeding and increased cardiovascular risk. These risks preclude endorsing either medication for primary or secondary prevention of colorectal cancer.