The ABCs of PNETs: Pancreatic neuroendocrine tumors
By Nicole Brudos Ferrara
According to the National Cancer Institute, a neuroendocrine tumor is a tumor that forms from cells that release hormones into the blood in response to a signal from the nervous system. Pancreatic neuroendocrine tumors (PNET) occur in the hormone-producing cells of the pancreas.
A rare tumor
"PNETs are less than 10% of pancreatic malignancies," says Thorvardur Halfdanarson, M.D., a medical oncologist at Mayo Clinic who specializes in neuroendocrine tumors. "We know there are probably 1 per 100,000 per year, so it's a rare tumor."
The American Cancer Society estimates that about 4,200 people in the U.S. will be diagnosed with pancreatic neuroendocrine tumors in 2021. The average age of diagnosis is 60, and pancreatic neuroendocrine tumors are slightly more common in men than women.
"Because patients with neuroendocrine tumors can live for many years, the prevalence of the tumors ― the number of patients actively dealing with the tumor at any given time ― is actually fairly high because the survival is much longer than for pancreatic adenocarcinomas," says Dr. Halfdanarson.
The occurrence of pancreatic neuroendocrine tumors seems to be on the rise. "We are increasingly seeing pancreatic neuroendocrine tumors diagnosed at early stages, oftentimes incidentally," says Dr. Halfdanarson. "Patients come in for reasons other than the tumor ― a CT for a kidney stone or something ― and there's a tumor in the pancreas."
The good news is that pancreatic neuroendocrine tumors diagnosed at an early stage have a higher survival rate.
Most pancreatic neuroendocrine tumors are cancerous, but they may or may not cause symptoms. When they cause symptoms, it's often because the tumors have grown large or spread. "Sometimes the tumors grow to be large and start causing pain by pushing on nerves of the pancreas," says Dr. Halfdanarson. "That part of the body is a busy place. There are a lot of nerves running up and down. There are blood vessels. So these tumors can start pushing on the nerves, causing pain."
Pancreatic neuroendocrine tumors also can spread, or metastasize, to the liver. "Sometimes patients have a pancreatic neuroendocrine tumor that has spread to the liver, and the liver's starting to fill up with metastases (new tumors). And that may cause pain on its own or abdominal fulness, or even a mass in the abdomen that the patient feels."
"Occasionally these tumors make hormones, and it's the hormones that make a person sick ― not the tumor itself," says Dr. Halfdanarson. Pancreatic neuroendocrine tumors can make insulin, causing a person's blood sugar to drop. These tumors also can make a hormone called gastrin that causes a person's stomach acid to increase, resulting in stomach ulcers and diarrhea. Despite arising from hormone-producing cells, pancreatic neuroendocrine tumors rarely produce enough hormones to cause such symptoms.
Treatment options offer hope
Treatment for pancreatic neuroendocrine tumors varies based on the types of cells involved in the cancer and the stage of the cancer. "For the early-stage PNET patients who have small tumors, low-grade tumors, as seen on a biopsy, we can sometimes wait and we don't always have to operate," says Dr. Halfdanarson.
A new and promising treatment is lutetium (Lu) 177 DOTATATE, a peptide receptor radionuclide therapy (PRRT) that the Food and Drug Administration approved in January 2018 to treat gastroenteropancreatic neuroendocrine tumors. The tumor-targeting DOTATATE in this peptide receptor radionuclide therapy binds to receptors on the cancer cells. Once it binds to the cancer cells, the lutetium 177 delivers a dose of radiation, damaging the cancer cell.
"Essentially, it's a drug that recognizes tumor cells," says Dr. Halfdanarson. "This treatment results in tumor shrinkage in probably as high as 20% to 30% of patients. The treatment is well-tolerated. It's very safe. And it stabilizes the tumor in most patients, sometimes even for years."
Dr. Halfdanarson urges people diagnosed with pancreatic neuroendocrine tumors to find a health care provider with experience diagnosing and treating a lot of these rare tumors. "Patients with neuroendocrine tumors who are seen at large-volume, specialized centers seem to do better than the average patients out there," he says.
Watch Dr. Halfdanarson discuss pancreatic neuroendocrine tumors in this video:
See also this article: "Innovative Therapy Improves Lives of People With Neuroendocrine Tumors."