Several types of cancer can start in the colon or rectum:1. Adenocarcinomas: More than 95% of colorectal cancers are a type of cancer known as adenocarcinomas. These cancers start in cells that form glands that make mucus to lubricate the inside of the colon and rectum. When doctors talk about colorectal cancer, this is almost always what they are referring to.
2. Carcinoid tumors: These tumors start from specialized hormone-producing cells of the intestine.
3. Gastrointestinal stromal tumors (GISTs): These tumors start from specialized cells in the wall of the colon called the interstitial cells of Cajal. Some are benign (non-cancerous); others are malignant (cancerous). These tumors can be found anywhere in the digestive tract, but they are unusual in the colon.
4. Lymphomas: These are cancers of immune system cells that typically start in lymph nodes, but they may also start in the colon, rectum, or other organs.