Colorectal cancer is a malignant neoplasm that affects the larger, lower portion of the intestinal tract. About two-thirds of such cancers occur in the colon, mainly in the sigmoid portion, and one-third occur in the rectum or at the recto-sigmoid junction. The third-leading cause of cancer morbidity and the second leading cause of cancer mortality, colorectal cancer has recently declined among white persons in the United States but is almost 50 percent higher, and rising, among African Americans. Hispanics have only half the mortality rate of non-Hispanic white persons. An estimated 135,400 new cases and 56,700 deaths are anticipated during 2001 in the United States. Risk factors for the disease include being older and male; having had polyps, inflammatory bowel disease, or previous other cancers; being physically inactive and obese; consuming excessive alcohol; and a low fiber diet. Five-year survival has recently been 62 percent among white persons and 53 percent among African Americans.
Worldwide, colorectal cancer amounts to about one-tenth of all cancers—almost 600,000 of the6.35 million cases of cancer that occur. Migrants to the United States tend to develop colorectal cancer rates that are similar to those among long-term residents of their adoptive country—even during the first generation or within twenty years of living in the United States. This relatively rapid change suggests the importance of lifestyle in the causation of the disease. This inference is further supported by the fact that colorectal cancer rates throughout the world tend to be substantially higher in urban areas than in rural areas in various countries.
Polyps in the colon, particularly multiple polyps and those exceeding 1.0 cm in diameter frequently precede the occurrence of malignant neoplasm; they therefore constitute a major risk factor.
Control measures include diet, screening, and treatment. It appears that a low fat diet that includes large amounts of vegetables and fruit reduces the risk of colorectal cancer, although the evidence is equivocal, especially as to the extent of reduction. Efforts to control the disease (e.g., the National Colorectal Cancer Awareness Month, supported by the Centers for Disease Control and Prevention of the United States Public Health Services), have recently been emphasizing screening by digital rectal examination (DRE), which is used to detect malignancies that can be reached by that means: the fecal occult blood test (FOBT); and sigmoidoscopy. Barium enemas and proctoscopy have also been used for screening, as well as diagnostically. In 1999 only two-fifths of the American people over fifty years of age had ever received the FOBT or sigmoidoscopy, the latter term including a colonoscopy, which reaches farther into the colon, and a proctoscopy, which extends only into the rectum. The FOBT is recommended annually after age fifty and sigmoidoscopy every five years. Sigmoidoscopy is particularly intended to disclose polyps which may evolve into cancer as well as malignancies that are already present. Both tests are somewhat awkward for patients, but are now recognized as important tools for controlling colorectal cancer. In several trials, biennial screening with FOBT among persons forty-five to eighty years of age reduced mortality from colorectal cancer by 15 to 21 percent; among persons over forty-five years of age, sigmoidoscopy reduced mortality in the distal colon by 59 to 79 percent.
The Office of Public Health and Science of the United States Department of Health and Human Services has set, as a goal for 2010, reduction of the colorectal mortality rate (age-adjusted) from 12.8 per 100,000 (in 1995) to 8.8 per 100,000.