Cancer starts when cells in the body begin to grow out of control. Cells in nearly any part of the body can become cancer, and can spread to other areas of the body. To learn more about how cancers start and spread, see What Is Cancer?
Pancreatic cancer begins when cells in the pancreas start to grow uncontrollably. The pancreas is an organ located behind the stomach. It is shaped a bit like a fish with a wide head, a tapering body, and a narrow, pointed tail. In adults it is about 6 inches long but less than 2 inches wide. The head of the pancreas is on the right side of the abdomen (belly), behind where the stomach meets the duodenum (the first part of the small intestine). The body of the pancreas is behind the stomach, and the tail of the pancreas is on the left side of the abdomen next to the spleen.
The pancreas has 2 main types of cells:
- Exocrine cells: Most of the cells in the pancreas form the exocrine glands and ducts. The exocrine glands make pancreatic enzymes that are released into the intestines to help you digest foods (especially fats). The enzymes are first released into tiny tubes called ducts. These merge to form larger ducts, which empty into the pancreatic duct. The pancreatic duct merges with the common bile duct (the duct that carries bile from the liver), and empties into the duodenum (the first part of the small intestine) at the ampulla of Vater.
- Endocrine cells: Endocrine cells make up a much smaller percentage of the cells in the pancreas. These cells are in small clusters called islets (or islets of Langerhans). The islets make important hormones like insulin and glucagon (which help control blood sugar levels), and release them directly into the blood.
Types of pancreatic cancer
The exocrine cells and endocrine cells of the pancreas form different types of tumors. It’s 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 with different tests, are treated in different ways, and have different outlooks.
Exocrine pancreatic cancers
Exocrine cancers are by far the most common type of pancreas cancer. If you are told you have pancreatic cancer, it is most likely an exocrine pancreatic cancer.
Pancreatic adenocarcinoma: About 95% of cancers of the exocrine pancreas are adenocarcinomas. These cancers usually begin in the ducts of the pancreas. Less often, they develop from the cells that make the pancreatic enzymes, in which case they are called acinar cell carcinomas.
Less common types of exocrine cancer: Other, less common exocrine cancers include adenosquamous carcinomas, squamous cell carcinomas, signet ring cell carcinomas, undifferentiated carcinomas, and undifferentiated carcinomas with giant cells.
Ampullary cancer (carcinoma of the ampulla of Vater): This cancer starts in the ampulla of Vater, which is where the bile duct and pancreatic duct come together and empty into the small intestine. Ampullary cancers aren’t technically pancreatic cancers, but they are included here because they are treated very similarly.
Ampullary 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 yellowing of the skin and eyes (jaundice). Because of this, these cancers are usually found earlier than most pancreatic cancers, and they usually have a better prognosis (outlook).
Pancreatic endocrine tumors (neuroendocrine tumors)
Tumors of the endocrine pancreas are uncommon, making up less than 5% of all pancreatic cancers. As a group, they are often called pancreatic neuroendocrine tumors (NETs) or islet cell tumors.
Pancreatic NETs can be benign (not cancer) or malignant (cancer). Benign and malignant tumors can look alike under a microscope, so it isn’t always clear if a pancreatic NET is cancer. Sometimes it only becomes clear that an NET is cancer when it spreads outside the pancreas.
There are many types of pancreatic NETs.
Functioning NETs: About half of pancreatic NETs make hormones that are released into the blood and cause symptoms. These are called functioning tumors. Each one is named for the type of hormone the tumor cells make.
- Gastrinomas come from cells that make gastrin. About half of gastrinomas are cancers.
- Insulinomas come from cells that make insulin. Most insulinomas are benign (not cancer).
- Glucagonomas come from cells that make glucagon. Most glucagonomas are cancers.
- Somatostatinomas come from cells that make somatostatin. Most somatostatinomas are cancers.
- VIPomas come from cells that make vasoactive intestinal peptide (VIP). Most VIPomas are cancers.
- PPomas come from cells that make pancreatic polypeptide. Most PPomas are cancers.
Most functioning NETs are gastrinomas or insulinomas. The other types are rare.
Non-functioning NETs: These tumors don’t make enough excess hormones to cause symptoms. They are more likely to be cancer than are functioning tumors. Because they don’t make excess hormones that cause symptoms, they can often grow quite large before they are found.
Carcinoid tumors: These NETs are much more common in other parts of the digestive system, although rarely they can start in the pancreas. These tumors often make serotonin (also called 5-HT) or its precursor, 5-HTP.
The treatment and outlook for pancreatic NETs depend on the specific tumor type and the stage (extent) of the tumor, but the outlook is generally better than that of pancreatic exocrine cancers.
Benign and precancerous growths in the pancreas
Some growths in the pancreas are simply benign (not cancer), while others might become cancer over time if left untreated (known as precancers). Because people are getting imaging tests such as CT scans more often than in the past (for a number of reasons), these types of pancreatic growths are now being found more often.
Serous cystic neoplasms (SCNs) (also known as serous cystadenomas) are tumors that have sacs (cysts) filled with watery fluid. SCNs are almost always benign, and most don’t need to be treated unless they grow large or cause symptoms.
Mucinous cystic neoplasms (MCNs) (also known as mucinous cystadenomas) are slow-growing tumors that have cysts filled with a jelly-like substance called mucin. These tumors almost always occur in women. While they are not cancer, some of them can progress to cancer over time if not treated, so these tumors are typically removed with surgery.
Intraductal papillary mucinous neoplasms (IPMNs) are benign tumors that grow in the pancreatic ducts. Like MCNs, these tumors make mucin, and over time they sometimes become cancer if not treated. Some IPMNs can just be followed closely over time, but some might need to be removed with surgery if they have certain features, such as if they are in the main pancreatic duct.
Solid pseudopapillary neoplasms (SPNs) are rare, slow-growing tumors that almost always develop in young women. Even though these tumors tend to grow slowly, they can sometimes spread to other parts of the body, so they are best treated with surgery. The outlook for people with these tumors is usually very good.
Last Revised: 04/05/2016