Colorectal cancer is the third most commonly diagnosed cancer and the second leading cause of cancer death in the United States. In 1996, an estimated 133,500 new cases of colorectal cancer were diagnosed and approximately 54,900 people died of the disease (American Cancer Society, 1996). Well-established risk factors for colorectal cancer include older age, male sex, inflammatory bowel disease, certain hereditary conditions, and a family history of colorectal cancer. However, these risk factors are not amenable to change. People with no predisposing factors are considered to be at average risk. About 75 percent of all colorectal cancer occurs in people with no known predisposing factors for the disease (Burt, Bishop, Lynch, et al., 1990).

Colorectal cancer incidence rises with age, beginning around age 40. Most patients (65 percent) present with advanced disease. The primary strategy for preventing colorectal cancer deaths is to detect and remove precursors of colorectal cancer or to detect and treat cancer in its earliest stages. Colorectal cancer screening tests have been shown to achieve accurate detection of early stage cancer and its precursors. Evidence exists that reduction in colorectal cancer mortality and morbidity can be achieved through detection and treatment of early-stage colorectal cancers and the identification and removal of adenomatous polyps - the precursors of colorectal cancer.

Most Americans are not screened for colorectal cancer. Information from the National Health Interview Survey (NHIS) indicated that in 1992 only 17.3 percent of people 50 years of age or older had undergone fecal occult blood testing in the previous year, and 9.4 percent had undergone sigmoidoscopy in the previous 3 years (Anderson and May, 1995; Brown, Potosky, Thompson, and Kessler, 1990). To estimate the prevalence of colorectal cancer screening practices, the Centers for Disease Control and Prevention (CDC) analyzed data on use of colorectal cancer screening methods from the 1992 and 1993 Behavior Risk Factor Surveillance System (CDC, 1996). That analysis documented low rates of use of colorectal cancer screening nationwide and underscored the need for efforts to increase screening.

Colorectal cancer survival is closely related to the clinical and pathological stage of the disease at diagnosis. Five-year survival for cancer limited to the bowel wall at the time of diagnosis approaches 90 percent (Mandel, Bond, Church, et al., 1993). Survival at 5 years is 35 to 60 percent when lymph nodes are involved and less than 10 percent with metastatic disease (Wingo, Tong, and Bolden, 1995).

There is a lack of consensus concerning the choice of screening and surveillance tests, the appropriate screening and surveillance intervals, and the cost-effectiveness of screening. This technical review summarizes the current evidence about colorectal cancer screening and highlights areas for future research to improve screening.