About 96% of all colorectal cancers are adenocarcinomas, derived from the mucus-secreting cells that line the inside of the colon and rectum. A variety of much less common tumors can also arise in the colon and rectum. These include carcinoid tumors, derived from hormone-secreting cells, and gastrointestinal stromal tumors, or GISTs, derived from interstitial cells in the walls of the GI tract. Other rare cancers that may arise in the colon or rectum include lymphomas, which arise in the colorectal lymph nodes, and sarcomas, which may arise from blood vessel, muscle, or connective tissue cells.