All types of pancreatic cancer begin when abnormal cells grow out of control within the pancreas. There are two types of cells in the pancreas, the exocrine cells and endocrine cells. These cells also have different functions. 

More than 95% of pancreatic cancers are classified as exocrine tumors. These tumors start in the exocrine cells that make pancreatic enzymes that help in digestion. Within this category, the vast majority of tumors are adenocarcinomas. The following table describes the different types of pancreatic exocrine tumors.

Accounting for less than 5% of all pancreatic tumors are neuroendocrine tumors, also called endocrine or islet cell tumors. Islet cells are the endocrine cells in the pancreas that produce and secrete the hormones insulin, glucagon and somatostatin into the bloodstream. Insulin and glucagon are the two main pancreatic hormones. Insulin lowers blood sugar levels while glucagon raises blood sugar levels. Together, these two main hormones work to maintain the proper level of sugar in the blood. Somatostatin regulates the levels of a variety of other hormones in the blood.

Pancreatic neuroendocrine tumors may be benign or malignant and they tend to grow slower than exocrine tumors. Pancreatic neuroendocrine tumors are either functional (produce hormones) or nonfunctional (produce no hormones). Most functional neuroendocrine tumors are benign. However, 90% of nonfunctional neuroendocrine tumors are cancerous. 

• Acinar Cell Carcinoma: Acinar cell carcinoma is a very rare form of pancreatic cancer that may cause excessive production of pancreatic lipase, the enzyme secreted to digest fats. Pancreatic lipase levels can be measured in the blood.
• Adenocarcinoma: Adenocarcinoma accounts for about 90% of all pancreatic cancers. It begins in cells lining the pancreatic duct. Adenocarcinomas may form glands, or a collection of cells surrounding an empty space.
• Adenosquamous Carcinoma: Adenosquamous carcinoma is similar to adenocarcinoma in that it forms glands, but it flattens as it grows. It can mimic other types of cancer that show squamous, or flattened, cell development.
• Giant Cell Tumor: Giant cell tumors are extremely rare and may not be as aggressive as adenocarcinoma. A giant cell tumor has unusually large cells, but the tumor is not any larger than other pancreatic cancers.
• Intraductal Papillary-Mucinous Neoplasm (IPMN): An IPMN grows from the main pancreatic duct or from side branches of the duct. The tumor may appear as a finger-like, or papillary, projection into the duct. An IPMN may be benign at the time of diagnosis. However, it has a high risk of progressing to malignancy. An IPMN may therefore be a precursor for adenocarcinoma.
• Mucinous Cystadenocarcinoma: Mucinous cystadenocarcinoma is a rare, malignant, spongy, cystic tumor. The cyst is filled with a thick fluid called mucin. It is similar to an IPMN, but occurs in just one area of the pancreas.
• Pancreatoblastoma: Pancreatoblastoma is a rare form of pancreatic cancer found primarily in children under the age of 10. It is often called “pancreatic cancer of infancy.”
• Serous Cystadenocarcinoma: Serous cystadenocarcinoma is a tumor that has progressed from a benign serous cystadenoma, characterized by many small cysts. They are extremely rare, accounting for less than 1% of pancreatic tumors.
• Solid and Pseudopapillary Tumors: Solid and pseudopapillary tumors can arise anywhere in the pancreas. Some parts of the tumor are solid, while other parts are papillary, or finger-like. These tumors are primarily found in women in their 30’s and are usually cured if completely removed with surgery.

Some rare forms of pancreatic cancer form from the abnormal growth of hormone-producing cells in the pancreas called islet cells. These tumors are known as pancreatic neuroendocrine tumors (pancreaticNETs or PNETs), pancreatic endocrine tumors or islet cell tumors.

Islet cells are the endocrine cells in the pancreas that produce and secrete the hormones insulin, glucagon and somatostatin into the bloodstream. Insulin and glucagon are the two main pancreatic hormones. Insulin lowers blood sugar levels while glucagon raises blood sugar levels. Together, these two main hormones work to maintain the proper level of sugar in the blood. Somatostatin regulates the levels of a variety of other hormones in the blood.

Pancreatic neuroendocrine tumors account for less than 5% of all pancreatic tumors. They may be benign or malignant and they tend to grow slower than exocrine tumors. Pancreatic neuroendocrine tumors are either functional (produce hormones) or nonfunctional (produce no hormones). Most functional neuroendocrine tumors are benign. However, 90% of nonfunctional neuroendocrine tumors are cancerous. The following table describes the different types of pancreatic neuroendocrine tumors.

• Gastrinoma (Zollinger-Ellison Syndrome): Gastrinomas overproduce gastrin. Most are malignant or have the ability to become malignant. When this tumor is inherited as part of a genetic syndrome called Multiple Endocrine Neoplasia Type 1 (MEN1) (see below), multiple tumors may be found in the head of the pancreas and/or the duodenum.
• Glucagonoma: Glucagonomas overproduce glucagon. They are usually large, often metastasize and about 70% are malignant. They are commonly found in the body and tail of the pancreas.
• Insulinoma: Insulinomas overproduce insulin. They are the most common pancreatic neuroendocrine tumors. They tend to be small and hard to find. Most of them are benign.
• Nonfunctional Islet Cell Tumor: Nonfunctional islet cell tumors are usually malignant. They are hard to detect.
• Somatostatinoma: Somatostatinomas overproduce somatostatin. They are extremely rare and usually very large. They can occur anywhere in the pancreas and in the duodenum. They vary in their potential to become malignant.
• Vasoactive Intestinal Peptide-Releasing Tumor (VIPoma or Verner-Morrison Syndrome): VIPomas overproduce vasoactive intestinal peptide (VIP). These tumors are usually located in the body and tail of the pancreas. Two-thirds of VIPomas are found in women. The syndrome is also known as Watery Diarrhea and Hypokalemia Achlorhydria (WDHA) Syndrome.
• Multiple Endocrine Neoplasia Type-1 (MEN1): MEN1 (also known as Wermer Syndrome) is a hereditary syndrome that causes multiple tumors in the parathyroid and pituitary glands, and the pancreas. It occurs when tumors are found in at least two of the three endocrine glands mentioned above. About 30-75% of people with MEN1 will develop pancreatic neuroendocrine tumors. Gastrinomas are the most common pancreatic neuroendocrine tumors in individuals with MEN1. The second most common are insulinomas. The tumors in the pancreas may be malignant and generally appear in individuals in their 30’s and 40’s.