The Normal Pancreas

The pancreas is an organ located behind the stomach. It is shaped a little bit like a fish with a wide head, a tapering body, and a narrow-pointed tail. It is about 6 inches long but less than 2 inches wide and extends horizontally across the abdomen. The head of the pancreas is on the right side of the abdomen, behind the place where the stomach meets the duodenum (the first part of the small intestine). The body of the pancreas is located behind the stomach and the tail of the pancreas is on the left side of the abdomen next to the spleen.

The pancreas contains 2 different types of glands: exocrine and endocrine.

The exocrine glands make pancreatic "juice," which is released into the intestines. This juice contains enzymes that help you digest fats, proteins, and carbohydrates in the food you eat. Without these, some of the food you eat would just pass through your intestines without being absorbed. The enzymes are released into tiny tubes called ducts. These tiny ducts merge together to form larger ducts that carry the pancreatic juice to the small intestine. More than 95% of the cells in the pancreas are exocrine glands and ducts.

A small percentage of the cells in the pancreas are endocrine cells. These cells are arranged in small clusters called islets (or islets of Langerhans). The islets release 2 important hormones, insulin and glucagon, directly into the blood. Insulin reduces the amount of sugar in the blood, while glucagon increases it. Diabetes results from a defect in insulin production.

Types of Tumors of the Pancreas

The exocrine cells and endocrine cells of the pancreas form completely different types of tumors.

Exocrine Tumors

These are far and away the most common type of pancreas cancer. Although benign (non-cancerous) cysts and benign tumors called cystadenomas can occur, most pancreatic exocrine tumors are malignant.

About 95% of cancers of the exocrine pancreas are adenocarcinomas. Adenocarcinomas usually begin in the ducts of the pancreas, but they sometimes develop from the cells that make the pancreatic enzymes (acinar cell carcinomas).

Less common types of ductal cancers of the exocrine pancreas include adenosquamous carcinomas, squamous cell carcinomas, and giant cell carcinomas. These types are distinguished from one another based on how they look under the microscope.

But the type of exocrine pancreatic cancer isn't as important as the stage (extent) of the cancer when it comes to treatment. The treatment of an exocrine pancreatic cancer is mostly based on the stage of the cancer, not its exact type. (Pancreatic cancer staging is described later in this document.)

A special type of cancer, called ampullary cancer (or carcinoma of the ampulla of Vater) deserves mention here. This cancer develops where the bile duct and pancreatic duct come together and empty into the duodenum. These cancers often block the bile duct while they are still small and have not spread far. This blockage causes bile to build up in the body, which leads to a yellowing of the skin and eyes (jaundice) and can turn the urine dark. This easily recognized sign alerts people that something is wrong. Because of this, ampullary cancers are usually found at an earlier stage than most pancreatic cancers, which means they usually have a better outlook than typical pancreatic cancers.

Ampullary cancers are included together with pancreatic cancer in this document because their treatments are very similar.

• insulinomas arise from cells that make insulin 
• glucagonomas come from cells that make glucagon 
• gastrinomas come from cells that make gastrin 
• somatostatinomas come from cells that make somatostatin 
• VIPomas come from cells that make vasoactive intestinal peptide (VIP)

These tumors are called "functioning" if they make hormones or "non-functioning" if they do not. Most functioning islet cell tumors are benign, while non-functioning tumors are more likely to be malignant. Malignant tumors are called islet cell cancers or islet cell carcinomas. Treatment and prognosis (outlook) depends on the specific type and stage (extent) of the tumor.

It is very important to distinguish between exocrine and endocrine cancers of the pancreas. They have distinct risk factors and causes, have different signs and symptoms, are diagnosed using different tests, are treated in different ways, and have different prognoses (outlooks).

The remaining sections of this document refer only to exocrine pancreatic and ampullary cancers.