The appendix is a small hollow tube attached to the large colon (the large colon is also called large bowel or large intestine). The appendix is approximately 4 inches long and shaped like a worm. The appendix serves no known purpose, although it is thought to possibly play a role in the immune system. Very rarely, the appendix may become cancerous. Since the appendix is attached to the colon, appendix cancer is considered a type of colorectal cancer. Colorectal cancers are also part of a larger group of cancers of gastrointestinal tract, or GI cancers.
Cancer of the appendix may cause appendicitis or cause the appendix to rupture. Sometimes this is the first symptom of appendix cancer. A ruptured appendix may cause a very serious condition called peritonitis, which is an infection of the lining of the abdomen and pelvis. A cancerous tumor of the appendix may also "seed" the abdomen with cancer cells. This may cause more cancerous tumors to develop in the abdomen before it is discovered. See Peritoneal Surface Malignancies and Peritoneal Carcinomatosis. Many times there are no symptoms of appendix cancer until it has progressed and is advanced. Abdominal discomfort and bloating of the abdomen can be signs of advanced appendiceal cancer
There are five most common (though still VERY rare) varieties of appendix cancer: Malignant Carcinoid, Mucinous Adenocarcinoma, Adenocarcinoma, Adenocarcinoid, and Signet Ring Adenocarcinoma. To learn more about these varieties of appendix cancer, treatment and prognosis, click the links here or on the left side of this screen.
Diagram of the stomach, colon and rectum from public domain source at http://www.cancer.gov/cancerinfo/wyntk/colon-and-rectum