Islet Cell Tumor

Overview

Function of the pancreas

The pancreas is a pear-shaped gland located in the abdomen between the stomach and the spine. It is about six inches in length and is composed of two major components:

• The exocrine component, made up of ducts and acini (small sacs on the end of the ducts), produces enzymes (specialized proteins) that are released into the small intestine to help the body digest and break down food, particularly fats.
• The endocrine component of the pancreas is made up of specialized cells clustered together in islands within the organ, called islets of Langerhans. These cells produce specific hormones, with the most important one being insulin, a substance that helps control the amount of sugar in the blood.

Types of pancreatic cancer

Cancer begins when normal cells begin to change and grow uncontrollably, forming a mass called a tumor. A tumor can be benign (noncancerous) or malignant (cancerous, meaning it can spread to other parts of the body).
The most common type of pancreatic cancer is called ductal adenocarcinoma, or simply, adenocarcinoma. In this type, the cancer begins in the exocrine component.

Much less commonly, tumors can begin in the islets of Langerhans, the endocrine component. An islet cell tumor can also be called a pancreatic islet cell tumor, pancreatic endocrine tumor, Islet of Langerhans tumor, or neuroendocrine tumor. The rest of this section focuses on islet cell tumors.

Subtypes of islet cell tumors

An islet cell tumor can be either benign or cancerous. Also, an islet cell tumor may be classified as either functioning or nonfunctioning. The term functioning means that the tumor cells produce hormones that cause specific symptoms, while a nonfunctioning islet cell tumor does not produce hormones.

There are five major classifications of functioning islet cell tumors:

Gastrinoma. A gastrinoma describes an islet cell tumor that produces a large amount of gastrin, a hormone that causes an excess amount of acid to be made in the stomach. This results in a condition called Zollinger-Ellison syndrome.

Insulinoma. This type of tumor produces too much insulin, resulting in hypoglycemia (low blood sugar). An insulinoma is more likely to be benign; only 10% become malignant.

Glucagonoma. A glucagonoma is an islet cell tumor that produces too much of the hormone glucagon. In contrast to an insulinoma, a glucagonoma causes hyperglycemia, a condition where there is too much sugar in the blood.

VIPoma. A VIPoma arises from cells in the pancreas that produce vasoactive intestinal peptide (VIP), a hormone that plays a role in water transport in the intestines. Excessive amounts of VIP can cause chronic, watery diarrhea, which causes a condition called Verner-Morrison syndrome.

Somatostatinoma. A somatostatinoma is a tumor that usually develops in the head of the pancreas. A somatostatinoma may produce somatostatin, a hormone that inhibits the secretion of several other hormones (such as growth hormone, insulin, and gastrin).

There is one major classification of nonfunctioning islet cell tumors:

Nonfunctioning tumors. Nonfunctioning tumors make up the majority of islet cell tumors. They produce none of the clinical symptoms or syndromes described above. As a result, they are typically diagnosed at more advanced stages of disease.