The normal pancreas
The pancreas is a slender organ which stretches across the upper abdomen. It is shaped a little 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 functions: exocrine and endocrine.
The exocrine portion of the pancreas makes pancreatic “juice,” which is released into the intestines. This juice contains enzymes that help you digest certain foods. Without these, some of the food would just pass through your intestines without being absorbed. The enzymes are transported to the intestine through a tiny tube called the pancreatic duct. These tiny ducts 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 the pancreatic juice into the duodenum (the first part of the small intestine) at the ampulla of Vater. More than 95% of the cells in the pancreas are in the exocrine glands and ducts.
The endocrine portion of the pancreas functions to produce hormones that primarily regulate blood sugar. It is continuous sampling the sugars levels in the blood and releasing insulin to help bring the blood sugar down or glucagon to bring it up. Problems with this regulation can lead to diabetes.
Benign and precancerous growths in the pancreas / Pancreatic Cysts
Not all growths in the pancreas are cancer. Some growths are simply benign (not cancer), while others might become cancer over time if left untreated (known as precancers). Because imaging tests such as CT scans and MRIs more sensitive than in the past , these types of pancreatic growths are now being found more often.
Serous cystic neoplasms (SCNs) (also known as serous cystadenomas or serous microcystic adenomas) are tumors that have sacs (cysts) filled with watery fluid. SCNs are benign with virtually no risk of becoming cancer. Most do not need to be removed but may 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 usually start in the body or tail of the pancreas and occur mostly in women. While they are not cancer, some of them can progress to cancer over time if not treated. These tumors often removed but can sometimes be followed closely over time depending on several factors, such as their size, rate of growth, how they look on imaging tests, and if they are causing symptoms.
Intraductal papillary mucinous neoplasms (IPMNs) are benign tumors that grow in the pancreatic ducts. Like MCNs, these tumors make mucin, and they can sometimes become cancer over time if not removed. When they start in the main pancreatic duct, the risk of becoming cancer may be as high as 40-60%; therefore they are often removed. Some IPMNs that start in a smaller branch of the pancreatic duct may be at increased risk of developing into cancer and also require removal. Most, however, can just be followed closely over time with CT or MRI if they do not have concerning features.
The exocrine cells and endocrine cells of the pancreas can 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 using different tests, are treated in different ways, and have different outlooks. Common to all of these tumors is the need for surgical removal in order for them to be cured.
Exocrine tumors are by far the most common type of pancreas cancer (95%). When someone says that they have pancreatic cancer, they usually mean an exocrine pancreatic cancer. These are referred to as adenocarcinomas.
Pancreatic adenocarcinoma: An adenocarcinoma is a cancer that starts in gland cells.. These cancers usually begin in the ducts of the pancreas. But sometimes they develop from the cells that make the pancreatic enzymes, in which case they are called acinar cell carcinomas.
Less common types of cancers: Other cancers of the exocrine pancreas include adenosquamous carcinomas, squamous cell carcinomas, signet ring cell carcinomas, undifferentiated carcinomas, and undifferentiated carcinomas with giant cells. These types are distinguished from one another based on how they look under the microscope although their treatment is often similar to pancreatic adenocarcinoma.
Solid pseudopapillary neoplasms (SPNs): These are rare, slow-growing tumors that almost always occur 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.
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 treated very similar to pancreatic adenocarcinoma.
Based upon the location of the pancreas, tumors are often able to grow in silence without the patient knowing anything is wrong. For slow-growing tumors or cysts, this can result in very large tumors by the time they are found. However, in more aggressive tumors such as pancreatic adenocarcinoma, this can lead to the cancer spreading before being discovered. The type of symptoms often depends on the location of the tumor. When they start in the left side of the pancreas (body or tail), symptoms are often very vague, such as dull abdominal or back pain, a “full” sensation when eating, or unintentional weight loss. However, a tumor starting in the head of the pancreas on the right side can block the bile duct. This results in bile backing up into the liver and causing jaundice where the skin and eyes turn yellow, the urine turns very dark, the stool can turn whitish in color, and itching of the skin can occur. Sometimes patients can develop diabetes unexpectedly up to a year before being diagnosed with pancreatic cancer.
Tumors of the endocrine pancreas are uncommon, making up less than 4% of all pancreatic cancers. As a group, they are sometimes known as pancreatic neuroendocrine tumors (NETs) or islet cell tumors.
Pancreatic NETs can be benign or malignant (cancer). Benign and malignant tumors can look alike under a microscope, so it isn’t always clear whether or not a pancreatic NET is cancer. Sometimes the diagnosis only becomes clear when the tumor spreads outside of the pancreas.
There are many types of pancreatic NETs.
Functioning tumors: 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 being made that leads to symptoms:
Gastrinomas produce a hormone called gastrin which is typically made in the stomach.Too much gastrin leads to over production of acid in the stomach resulting in ulcers and diarrhea. Gastrinomas are commonly considered cancers.
Insulinomas make an abundance of insulin. This results in low blood sugars which can cause people to feel jittery, confused, or pass out. Most insulinomas are benign (not cancers).
Glucagonomas make glucagon which causes diabetes and skin rashes. Glucagonomas are rare tumor that are usually cancers.
Somatostatinomas make a hormone called somatostatin. This hormone blocks the effects of other hormones so can have many symptoms. Most somatostatinomas present with pain, however, and are usually cancers.
VIPomas produce a hormone called vasoactive intestinal peptide (VIP). These extremely rare tumors cause severe diarrhea and are usually cancers.
The most common types of functioning NETs are gastrinomas and insulinomas. The other types occur very rarely.
Non-functioning tumors: These tumors often make hormones but not in amounts that cause symptoms. Because they don’t make excess hormones that cause symptoms, they can often grow quite large or spread to other organs before they are found.
Carcinoid tumors: These are another type of NET that can start anywhere in the digestive system including the pancreas but most commonly start in the intestines. These tumors often make serotonin (also called 5-HT) or its precursor, 5-HTP which can lead to carcinoid syndrome where people have flushing in the skin of the face or chest and profuse diarrhea.
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.