Epidemiology 

Colorectal cancer is the third most frequently diagnosed cancer among both men and women (over 140,000 new cases) and the third leading cause of cancer death (nearly 50,000 deaths) each year in the United States. The lifetime risk of diagnosis with colorectal cancer is about 5%, while the lifetime risk for dying from colorectal cancer is about 2%. The good news is that U.S. incidence and mortality rates have been gradually but steadily declining over the past three decades. These trends are attributed to changes in risk factor prevalence, such as decreased tobacco use; increased screening, which both prevents cancers and increases detection of early-stage curable cancers; and improved treatment.

Risk Factors

The strongest risk factors for colorectal cancer are: increasing age; personal history of colorectal cancer, adenomatous polyps, or longstanding inflammatory bowel disease; and family history of colorectal neoplasia—particularly those with affected multiple first-degree relatives, a single first-degree relative diagnosed before age 60 years, or a hereditary colorectal cancer syndrome. Weaker risk factors include male sex, African American race, tobacco use, excessive alcohol use, red meat consumption, and obesity. Aside from age, persons without any strong risk factors are considered average risk—even if they have some of the weak risk factors. Overall, 90% of new cases and 94% of deaths occur after age 50 years52; the median age at diagnosis is 68 years and the median age at death is 74 years.50 While the lifetime risk of colorectal cancer is extremely high in patients with hereditary syndromes, about 75% of 

colorectal cancers arise in people without any obvious hereditary risk or common exposures among family members.

Prevention

The most effective prevention strategy is to screen for and remove pre-cancerous adenomatous polyps. Screening programs using fecal blood testing or flexible sigmoidoscopy have been shown in randomized trials to reduce the risk of developing colorectal cancer by about 15% to 20%. Physical activity, aspirin and nonsteroidal anti-inflammatory drugs (NSAIDs), and postmenopausal combined hormone replacement therapy (estrogen and progestin) are also associated with decreased risk of colorectal cancer. However, the USPSTF recommends against routinely using aspirin and NSAIDs for prevention in average-risk persons because the potential harms, including GI bleeding, hemorrhagic stroke, and renal impairment, outweigh the benefits (grade D). Hormone therapy for cancer chemoprevention is not advised; women receiving combined therapy were actually more likely to present with advanced-staged colorectal cancers and appear to have a higher risk for colorectal cancer mortality. Furthermore, hormone therapy is associated with increased risk of breast cancer, cardiovascular events, and venous thromboembolism. There has been no convincing evidence that dietary changes or taking supplements can prevent colorectal cancer.