What are islet cell tumors?

An islet cell tumor is a mass of abnormal cells that forms in the endocrine (hormone-producing) tissues of the pancreas. Islet cell tumors may be benign (noncancer) or malignant (cancerous). Islet cell cancer is rare.

The pancreas is about 6 inches long and is shaped like a thin pear, wider at one end and narrower at the other. The pancreas lies behind the stomach, inside a loop formed by part of the small intestine. The broader right end of the pancreas is called the head, the middle section is called the body, and the narrow left end is the tail.

The pancreas has two basic jobs in the body. It produces digestive juices that help break down (digest) food, and hormones (such as insulin) that regulate how the body stores and uses food. The area of the pancreas that produces digestive juices is called the exocrine pancreas. About 95% of pancreatic cancers begin in the exocrine pancreas. The hormone-producing area of the pancreas has special cells called islet cells and is called the endocrine pancreas. Only about 5% of pancreatic cancers start here. This summary has information on cancer of the endocrine pancreas (islet cell cancer). (See the PDQ summary on Pancreatic Cancer Treatment for more information on cancer of the exocrine pancreas.)

The islet cells in the pancreas make many hormones, including insulin, which help the body store and use sugars. When islet cells in the pancreas become cancerous, they may make too many hormones. Islet cell cancers that make too many hormones are called functioning tumors. Other islet cell cancers may not make extra hormones and are called nonfunctioning tumors. Tumors that do not spread to other parts of the body can also be found in the islet cells. These are called benign tumors and are not cancer. A doctor will need to determine whether the tumor is cancer or a benign tumor.

A doctor should be seen if there is pain in the abdomen, diarrhea, stomach pain, a tired feeling all the time, fainting, or weight gain without eating too much.

If there are symptoms, the doctor will order blood and urine tests to see whether the amounts of hormones in the body are normal. Other tests, including x-rays and special scans, may also be done.

The chance of recovery (prognosis) depends on the type of islet cell cancer the patient has, how far the cancer has spread, and the patient’s overall health.