Popular Common Cancers
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.