What Are Neuroendocrine Tumors?

Once considered rare, the incidence of neuroendocrine tumors (NETs) has risen over the past few decades. More than 100,000 people in the United States have neuroendocrine tumors, which exceeds the incidence of both pancreatic cancer and stomach cancer in the U.S.

NETs are tumors that originate from neuroendocrine cells, which are cells found throughout the body that can release hormones into the bloodstream. NETs can be benign or malignant, and are also classified as either a pancreatic neuroendocrine tumor or a carcinoid tumor, based on where the tumor originates. Pancreatic neuroendocrine tumors start in the pancreas, and carcinoid tumors originate in other places throughout the body, including the appendix, small intestine, and lungs.

Symptoms vary depending upon the types of NET and its location. Some patients may experience symptoms caused by the presence of the tumor and its effect on nearby normal organs. For instance, tumors in the lungs may cause a persistent cough or hoarseness. Tumors in the small intestine or pancreas may cause abdominal pain.

Some patients experience symptoms related to hormones secreted by NETs. Symptoms will depend on which hormone is produced. Carcinoid syndrome, which is most common in patients with small intestine NETs, is caused by production of hormones including serotonin, which can lead to flushing and diarrhea.

Some pancreatic neuroendocrine tumors can also produce a variety of hormones, including

  • Gastrin – which can cause high acid levels and stomach ulcers
  • Insulin – which can cause low blood sugar levels
  • Glucagon – which can cause skin rash and high blood sugar levels
  • Vasoactive intestinal peptide (VIP) – which can cause diarrhea

What causes neuroendocrine tumors?

In most cases, there is no clear cause of NETs. Researchers at the Neuroendocrine and Carcinoid Tumors Program at Dana-Farber/Brigham and Women’s Cancer Center are investigating genetic and environmental causes. There does not appear to be a strong association between cases of these tumors and typical cancer risk factors such as smoking and exposure to environmental toxins. In rare cases, NETs can be linked to hereditary conditions such as multiple endocrine neoplasia types 1 and 2 and Von-Hippel Lindau disease.

How are neuroendocrine tumors treated?

As with most cancers, treatment for NETs depends on the individual patient and how advanced the disease is. In early stages, treatment usually involves surgery to remove the tumor. In these cases, follow-up chemotherapy and radiation are usually not required, though patients are typically monitored with scans and blood tests following surgery.

In cases where the cancer has spread, doctors may recommend somatostatin analogs, targeted therapies, or chemotherapy. Somatostatin analogs can reduce hormone secretion by NETs and help slow tumor growth. When the tumor has spread to the liver, NETs may be treated with liver-directed therapies that can block blood supply to the growths in the liver.