Key Points

• Average-risk individuals should begin colorectal cancer screening at age 50, and at age 45 in African Americans.

Colorectal cancer (CRC) is the third leading cause of cancer mortality in the United States, accounting for an estimated 9% of all cancer deaths in 2009. Risk factors include increasing age, a family history of CRC, obesity, sedentary lifestyle, a diet high in red meat and low in vegetables, and excessive alcohol and/or tobacco use. Diets high in fiber, fruits, vegetables, and calcium may be protective, but data are inconclusive. African Americans have a 50% higher likelihood of dying from CRC than Caucasians, because they may have more proximal distribution of colonic adenomas and carcinomas than the general population, and these may be missed more often on suboptimal screening (ACS, 2009).

Approximately 75% of CRCs are diagnosed in individuals who have no risk factors other than advanced age; 90% of patients are older than 50. Other risk factors include prior or family history of CRC or adenomatous polyps, chronic IBD, and genetic syndromes. Several case-control and cohort studies found an inverse association between physical activity and risk in men and women of all ages and in various racial and ethnic groups in diverse geographic areas worldwide. The long-term use of aspirin may be associated with a decreased risk of CRC, yet the risk/benefit profile for chemo-prevention cannot justify broad recommendations for its use in the general population (Nease, 2004).

Up to 30% of CRCs are believed to arise secondary to a genetic predisposition. Approximately 20% of cases occur among patients who have a history of CRC in a first-degree relative. About 6% are attributable to identifiable, inherited genetic mutations known as hereditary colorectal cancer syndromes, including familial adenomatous polyposis (FAP) and hereditary nonpolyposis colorectal cancer (HNPCC). Although these syndromes are relatively uncommon, they confer a lifetime risk of CRC ranging from 80% to 100%.

Currently accepted methods for screening of CRC include the digital rectal examination (DRE), fecal immunochemi-cal test (FIT), double-contrast barium enema (DCBE), flexible sigmoidoscopy, and colonoscopy. According to the AGA, "the relative virtues of each screening test can be debated, but the best test is that one that gets done" (Burt et al., 2004). Screening should begin by classifying a patient's level of risk based on personal, family, and medical history, which together determine the approach to screening in that person. Box 38-9 details current CRC screening recommendations.

The DRE is a simple, inexpensive, and minimally invasive test that can be routinely performed in the office during yearly health maintenance examinations. It allows for palpation of the internal anal canal and examination of the prostate. Along with DRE, FIT should be performed to assess for occult blood. The DRE itself has a very low diagnostic yield, identifying less than 10% of colorectal tumors. Sensitivity of DCBE varies widely, ranging from 50% to 80% for polyps less than 1 cm, 70% to 90% for polyps greater than 1 cm, and 55% to 85% for Dukes stage A and B colon cancers (Winawer et al., 1997). In a comparison study with colonoscopy, sensitivity of barium enema for neoplasia was significantly lower (32% for polyps <5 mm, 53% for polyps 0.6-10 mm, 48% for polyps >1 cm) (Winawer et al., 2000). Any suspected lesions identified by DCBE need to be confirmed, biopsied, and removed by colonoscopy. Rarely, the classic "apple core" hallmark sign of a colonic mass may be visualized on DCBE (Fig. 38-32).

Flexible sigmoidoscopy is an efficient screening tool for individuals at an average risk for CRC, allowing for direct visualization and biopsy of the colonic mucosa in the rec-tosigmoid, descending, and distal transverse colon. To date, no RCTs or case-control studies have shown that screening with this method decreases CRC mortality for tumors within the reach of the standard 60-cm scope. The limitation of this method is that advanced lesions may be missed in the ascending and proximal transverse colon in individuals who

Box 38-9 Current Colorectal Cancer (CRC) Screening Recommendations

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