This cancer begins when cells start growing abnormally in the pancreas, an organ about 6 inches long and 2 inches wide located behind the stomach. The pancreas contains two different types of glands: exocrine and endocrine.
Cancer that starts in the glandular cells of the exocrine and endocrine glands is called an adenocarcinoma.
Exocrine cells make up more than 95 percent of the cells in the pancreas and form the exocrine glands and duct.
The exocrine glands produce enzymes that help in food digestion. These glands release (excrete) these enzymes into the duodenum (first part of the small intestine) by way of ducts, or tiny tubes.
Cancerous (malignant) exocrine tumors are the most common type of pancreatic cancer. Although sometimes benign (noncancerous) tumors called cystadenomas grow in the exocrine glands, most often exocrine tumors are malignant (cancerous).
Cancers that start in the glandular cells (adenocarcinomas) usually begin in the tiny tubes (ducts) of the pancreas that excrete enzymes. However, exocrine cancer sometimes develops in the acinar cells that make the pancreatic enzymes and is called acinar cell carcinoma.
Less common types of ductal cancers of the exocrine pancreas include:
- Adenosquamous Carcinomas
- Squamous Cell Carcinomas
- Giant Cell Carcinomas
Doctors determine the stage of an exocrine pancreatic cancer, rather than its exact type, to devise a treatment plan. Staging involves determining how large the tumor is and how far the cancer has spread.
Ampullary Cancer (Carcinoma of the Ampulla of Vater)
The ampulla of Vater is the place where the bile duct from the liver and the pancreatic duct (which carries enzymes) merge together, emptying bile and enzymes into the duodenum (the first part of the small intestine).
Cancers that start in the ampulla of Vater are called ampullary cancers. These cancers often block the bile duct, causing the buildup of bile (a fluid that helps digest food fats for absorption by the body).
This leads to jaundice (the yellowing of the skin and eyes), which is a clear sign that something is wrong. Consequently, many ampullary cancers are often detected early when treatments are more effective, so they have a better prognosis (outlook) than typical pancreatic cancers.
A small percentage of the cells in the pancreas are endocrine cells, which are arranged in small clusters called islets (or islets of Langerhans). These islets (or endocrine glands) produce hormones that help the body use or store the energy that comes from food.
They are called "endocrine" because they release hormones, such as insulin and glucagon, directly into the blood stream, without using ducts. Insulin reduces and glucagon increases the amount of sugar in the blood. Diabetes occurs from a defect in insulin production.
Tumors of the endocrine part of the pancreas are not very common. As a group, they are known as pancreatic neuroendocrine tumors (NETs) or islet cell tumors.
About half of pancreatic NETs are called functioning tumors because they make hormones that are released into the blood. NETs that do not make hormones are called non-functioning.
There are several subtypes of NETs. Each is named according to the type of hormone-making cell it starts in.
- Insulinomas begin in the cells that make insulin.
- Glucagonomas begin in the cells that make glucagon.
- Gastrinomas begin in the cells that make gastrin.
- Somatostatinomas begin in the cells that make somatostatin.
- VIPomas begin in the cells that make vasoactive intestinal peptide (VIP).
- PPomas begin in the cells that make pancreatic polypeptide.
Carcinoid tumors are another type of pancreatic NET that often produce a neurotransmitter called serotonin (also called 5-HT) or its precursor, 5-HTP (a substance that will be made into 5-HT).
The most common types of pancreatic endocrine tumors are gastrinomas and insulinomas. The other types very rarely occur.
These pancreatic endocrine tumors (NETs) can be benign (noncancerous) or malignant (cancerous). Cancerous pancreatic neuroendocrine tumors make up less than 4 percent of all pancreatic cancers diagnosed.
Treatment and prognosis depend on the specific tumor type and the stage of the cancer. However, the prognosis for cancerous pancreatic neuroendocrine tumors (NETs) is generally better than that of pancreatic exocrine cancers.