Types of Colorectal Cancer

Colon Cancer vs. Rectal Cancer

Though both colon cancer and rectal cancer can be referred to as colorectal cancer, the difference lies in where the cancer actually began.

If the cancer began in the colon, which is the first four to five feet of the large intestine, it may be referred to as colon cancer. If the cancer began in the rectum, which is the last several inches of the large intestine leading to the anus, it is called rectal cancer.

Colorectal cancer starts in the inner lining of the colon and/or rectum, slowly growing through some or all of its layers. It typically starts as a growth of tissue called a polyp. A particular type of polyp called an adenoma can develop into cancer. 

Adenocarcinoma 

There are numerous types of colorectal cancer, but adenocarcinoma is the most common. A cancer of the intestinal gland cells, adenocarcinomas represent more than 95 percent of colon and rectal cancers. “Adeno” is the prefix for gland, and adenocarcinomas typically start within the intestinal gland cells that line the inside of the colon and/or rectum. They tend to start in the inner layer and then spread deeper to other layers. There are two main subtypes of adenocarcinoma: 

• Mucinous adenocarcinoma is made up of approximately 60 percent mucus. The mucus can cause cancer cells to spread faster and become more aggressive than typical adenocarcinomas. Mucinous adenocarcinomas account for 10 to 15 percent of all colon and rectal adenocarcinomas.
• Signet ring cell adenocarcinoma accounts for less than one percent of adenocarcinomas. Named for its appearance under a microscope, signet ring cell adenocarcinoma is typically aggressive and may be more difficult to treat.

Other Types of Colorectal Cancer

There are numerous other types of rare colorectal cancers, and combined these types account for just 5 percent of all cases. Below are examples of other colorectal types:

Gastrointestinal Carcinoid Tumors – This slow-growing cancer forms in the neuroendocrine cell (a nerve cell that also creates hormones) in the lining of the gastrointestinal tract. These tumors account for just 1 percent of all colorectal cancers, but half of all of the cancers found in the small intestine.

The neuroendocrine cells create hormones that help control digestive juices, as well as the muscles that are used to move food through the stomach and intestines. These types of tumors are most often found in the rectum, appendix or small intestine. A gastrointestinal carcinoid tumor can increase your risk of forming other cancers in the digestive system. Usually, a gastrointestinal carcinoid tumor will have no symptoms in the early stages, but carcinoid syndrome could occur if the cancer spreads to the liver or other parts of the body. Carcinoid syndrome could cause wheezing, flushing and diarrhea several times a day.

Primary Colorectal Lymphomas – A type of non-Hodgkin lymphoma (NHL), lymphomas are cancers that develop in the lymphatic system from cells called lymphocytes. Lymphocytes are a type of white blood cell that helps the body fight infections. NHL can develop in many parts of the body, including the lymph nodes, bone marrow, spleen, thymus and the digestive tract. Primary colorectal lymphomas account for just 0.5 percent of all colorectal cancers, and about 5 percent of all lymphomas. The disease usually occurs later in life, and is more common in men than women.

Gastrointestinal Stromal Tumors – Also known as GISTs, this is a rare type of colorectal cancer that starts in a special cell found in the lining of the gastrointestinal (GI) tract called interstitial cells of Cajal (ICCs). Under a microscope, GIST cells look similar to muscle or nerve cells. More than 50 percent of GISTs start in the stomach. While most of the others start in the small intestine, the rectum is the third most common location. GISTs are classified as sarcomas, cancers that begin in the connective tissues, which include fat, muscle, blood vessels, deep skin tissues, nerves, bones and cartilage.

Leiomyosarcomas – Another form of sarcoma, leiomyosarcomas essentially means “cancer of smooth muscle.” The colon and rectum have three layers of the type of muscle that can be affected, which all work together to guide waste through the digestive tract. This rare type of colorectal cancer accounts for about 0.1 percent of all colorectal cases.

Melanomas – Though most commonly associated with the skin, melanomas can occur anywhere, including the colon or rectum.

Squamous Cell Carcinomas – Some parts of the GI tract, like the upper part of the esophagus and the end of the anus, are lined with flat cells called squamous cells. These are the same type of cells that are found on the surface of the skin. Cancers starting in these cells are called squamous cell carcinomas.