How common are neuroendocrine tumors?
Although neuroendocrine tumors have historically been considered rare, the incidence of such tumors has been increasing in the past few decades. Recent statistics suggest that more than 100,000 people in the United States have neuroendocrine tumors — more than the number of people with other, better known cancers, like pancreatic or stomach cancer. This increase parallels increased awareness and knowledge about how to diagnose neuroendocrine tumors, as well as how to effectively treat them.
What causes neuroendocrine tumors?
In rare cases, neuroendocrine tumors may be familial. Certain inherited conditions, including multiple endocrine neoplasia types 1 and 2, Von-Hippel Lindau disease, and others, result in multiple family members being affected.
However, for the majority of neuroendocrine tumors (more than 95%), no clear cause has been identified. Traditional cancer risk factors, like exposure to environmental toxins or smoking, do not appear to be strongly associated with neuroendocrine tumors.
Our researchers are actively investigating potential environmental or genetic causes for neuroendocrine tumors.
Are there different types of neuroendocrine tumors?
Neuroendocrine tumors originate from neuroendocrine cells that can be found throughout the body. In some cases, these tumors have the ability to secrete hormones, which can cause specific and unique symptoms.
Neuroendocrine tumors can be classified according to their site of origin, usually either pancreatic neuroendocrine tumors (which start in the pancreas) or carcinoid tumors (which start in other organs). Carcinoid tumors most commonly start in the lungs, small intestine, appendix, or rectum.
- Pancreatic neuroendocrine tumors: Pancreatic neuroendocrine tumors may arise either sporadically, or less commonly, in patients with multiple endocrine neoplasia type I (MEN 1) and other inherited syndromes.
About one-third of pancreatic neuroendocrine tumors secrete hormones, including insulin, glucagon, gastrin, or vasoactive intestinal peptide.
- Carcinoid tumors:
Carcinoid tumors are usually classified based on their site of origin:
Neuroendocrine tumors, particularly those that start in the small intestine, can produce hormones such as serotonin, which leads to symptoms including flushing or diarrhea. These symptoms are referred to as carcinoid syndrome.
- Foregut tumors include bronchial and gastric carcinoid tumors.
- Midgut tumors include carcinoids tumors of the small intestine and appendix.
- Hindgut tumors include colon and rectal carcinoid tumors.
Bronchial carcinoids often cause symptoms of cough, wheezing, hemoptysis, and recurrent post-obstructive pneumonia.
Gastric carcinoids usually do not produce notable symptoms and are often found incidentally.
Small intestine carcinoids may cause symptoms of intermittent bowel obstruction that mimic irritable bowel syndrome. Appendiceal carcinoids are usually found incidentally. About 50% of rectal carcinoid tumors are asymptomatic and found during a routine endoscopy.
How are neuroendocrine tumors treated?
- Surgery: When neuroendocrine tumors are found at an early stage (before cancer has spread to other organs), they can usually be removed surgically. In most cases, treatment with chemotherapy or radiation therapy after surgery is not necessary, and patients can be monitored with blood tests and scans.
If the tumor has spread and surgery is not possible, a variety of different treatments can be used. These include:
- Liver-directed therapies: In some cases, the liver is the primary or only site where the neuroendocrine tumor has spread. Liver-directed therapy often involves embolization, an interventional radiology procedure to cut off the blood supply to the liver metastases, and can be very effective.
- Somatostatin analogs: Most neuroendocrine tumors have receptors for the hormone somatostatin. A number of synthetic somatostatin analogs, including octreotide and lanreotide, are available that mimic the action of somatostatin and can be used to treat these tumors. These drugs are usually highly effective in decreasing hormone production and can also help slow tumor growth.
- Chemotherapy: Chemotherapy has been used for many years as a treatment for neuroendocrine tumors, and in some cases can be highly effective, particularly for pancreatic neuroendocrine tumors. Drugs that are used include streptozocin and temozolomide.
- Targeted therapies: Unlike most traditional chemotherapy, targeted therapies are molecules that specifically target growth pathways in the tumor cells. In 2011, two targeted therapies were approved for use for pancreatic neuroendocrine tumors:
- Sunitinib targets angiogenesis (the process by which tumors grow new blood vessels).
- Everolimus targets a molecule called mTOR, which serves as a central signaling molecule for a number of cancer growth pathways. Everolimus was also approved in 2016 for the treatment of lung and gastrointestinal neuroendocrine tumors.
- Peptide receptor radionuclide therapy (PRRT): PRRT is a form of therapy that combines a somatostatin analog, which binds to the somatostatin receptor on neuroendocrine tumor cells, and a radionuclide that can deliver radiation to the tumor.