Where does pancreatic cancer start? The pancreas The pancreas is an organ located behind the stomach. Its shape resembles that of a fish, with a broad head, a broad to slender body and a narrow pointed tail. In adults, it is about 6 inches (15 centimetres) long and less than 2 inches (5 centimetres) wide. 

The most common type of pancreatic cancer, adenocarcinoma of the pancreas, occurs when exocrine cells in the pancreas begin to grow out of control. Most of the pancreas is made up of exocrine cells that form the exocrine glands and ducts. The exocrine glands produce pancreatic enzymes that are released into the intestine to help you digest food (especially fats). The enzymes are released into small tubes called ducts that eventually drain into the pancreatic duct. The pancreatic duct joins 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 make up a smaller percentage of the cells in the pancreas. These cells produce important hormones, such as insulin and glucagon (which help control blood sugar levels), and release them directly into the blood. Pancreatic neuroendocrine tumours arise from endocrine cells.