Colon cancer is cancer of the large intestine. Cancer that develops in the last eight to 10 inches of the colon is called rectal cancer; together they are often referred to as colorectal cancer. Colorectal cancer is the fourth most common cancer and the second leading cause of cancer-related deaths in the United States. In 2007, 112,340 cases of colon cancer were diagnosed in the United States (along with 41,420 cases of rectal cancer). There were 52,180 deaths from both rectal and colon cancer that year. Over 95 percent of colon cancer cases are adenocarcinomas, or cancer in the glands or secretory cells, that develop when a change occurs in the cells lining the colon or rectum. Colon cancer often begins as an abnormal, exaggerated tissue growth called an intestinal polyp or adenoma; these adenomatous polyps gradually become precancerous and then cancerous, and in later stages of colon cancer, they can spread to nearby lymph nodes and other organs.
While colorectal cancer is very common, when diagnosed early it is among the more treatable types of cancer. In fact, the five-year survival rate for patients whose colorectal cancers were diagnosed before the cancer spread is over 90 percent. However, only 37 percent of colorectal cancers are detected in this localized stage.