Ernest H. Rosenbaum, MD, Malin Dollinger, MD, and Michael A. Friedman, MD
Cancer of the large bowel, or colon and rectum—the last 7 ft. (2 m) of the intestine—is a highly treatable and often curable disease when it is localized and diagnosed in its early stages. But when it spreads through the bowel wall to lymph nodes or nearby organs, the chances for cure are reduced.
Thirteen percent of all cancers in the United States involve either the colon or the rectum. An estimated 149,000 colorectal cancers will be diagnosed in 1994, 107,000 in the colon and 42,000 in the rectum. Taken together, they are second only to lung cancer as a cause of cancer deaths in the United States (56,000 deaths).
These tumors may be common because about half the population over 40 are thought to have clumps of tissues protruding from the inner layer (mucosa) of the colon or rectum. These mushroom-like growths are called polyps, and while most are benign , at least one type—adenomatous polyps— may be a precursor to cancer. About 90 percent of colorectal cancers are thought to arise from these polyps, and a person with a colorectal adenoma runs three times the risk of developing colorectal cancer. Overall, the lifetime risk of developing colorectal cancer is 6 percent (one out of every 20 Americans).
The colon and the rectum look similar and are connected to each other—the rectum is the final 5 in. (12 cm) of the colon above the anus—but there are major differences in the way colon and rectal tumors are treated.
