Colorectal cancer is a cancer that starts in the colon or the rectum. These cancers can also be named colon cancer or rectal cancer, depending on where they start. Colon cancer and rectal cancer are often grouped together because they have many features in common. Most colorectal cancers are due to old age and lifestyle factors with only a small number of cases due to underlying genetic disorders.
Adenocarcinomas make up more than 95% of colorectal cancers. These cancers start in cells that form glands that make mucus to lubricate the inside of the colon and rectum. Other, less common types of tumors that start in the colon and rectum include:
Gastrointestinal stromal tumors start from specialized cells in the wall of the colon called the interstitial cells of Cajal. Some are non-cancerous. These tumors can be found anywhere in the digestive tract, but it is unusual to find them in the colon.
Lymphomas are cancers of immune system cells that typically start in lymph nodes, but they can also start in the colon, rectum, or other organs.
Sarcomas can start in blood vessels, muscle layers, or other connective tissues in the wall of the colon and rectum. Sarcomas of the colon or rectum are rare.