A type of cancer called adenocarcinoma accounts for more than 95 percent of cancers in the colon and rectum and is usually what is meant by the term "colorectal cancer." It is the type we focus on in this section. There are other types of cancer that can be found in the colon and rectum, but they are rare.
Here is an overview of the types of cancer in the colon and rectum:
Adenocarcinoma - Adenocarcinomas are tumors that start in the lining of internal organs. "Adeno" means gland. These tumors start in cells with glandular properties, or cells that secrete. They can form in many different organs, such as the lung or the breast. In colorectal cancer, early tumors start as small adenomatous polyps that continue to grow and can then turn into malignant tumors. The vast majority of colorectal cancers are adenocarcinomas.
Gastrointestinal stromal tumors (GIST) - These are tumors that start in the muscle tissue of the digestive tract, although they rarely appear in the colon. They can be benign (noncancerous) at first, but many do turn into cancer. When this happens, they are called sarcomas. Surgery is the usual treatment if the tumor has not spread.
Lymphoma - A lymphoma is a cancer that typically starts in a lymph node, which is part of the immune system. However, it can also start in the colon or rectum.
Carcinoids - Carcinoids are tumors that start in special hormone-producing cells in the intestine. Often they cause no symptoms. Surgery is the usual treatment.