Rectal cancer is cancer that develops in the rectum (the last eight to 10 inches of the colon or large intestine). Together, rectal and colon cancers are referred to as colorectal cancers, and they are the second leading cause of cancer deaths in the United States. Colorectal cancer is more often found in men than women, and in African Americans than members of other racial groups. It is also more common in developed countries (e.g., the U.S. and Japan) than in developing countries (such as those in Asia and Africa). In 2007, there were 41,420 diagnoses of rectal cancer in the United States; that year, 52,180 people died of either colon or rectal cancer.
About 95 percent of colorectal cancers are adenocarcinomas, a cancer of the glands or secretory cells that develops when there are changes in the cells lining the rectal or colon walls. Colorectal cancer cases often begin as intestinal polyps, or abnormal growths of tissue that can eventually become precancerous and then cancerous.