Neuroendocrine tumor

A neuroendocrine tumor (NET) is a rare type of tumor that arises from specialized body cells called neuroendocrine cells. These cells have traits of both nerve cells and hormone-producing cells, and release hormones into the blood in response to signals from the nervous system. Because a neuroendocrine tumor arises from cells that produce hormones, the tumor can also produce hormones.

Neuroendocrine tumors can develop anywhere in the body, but most occur in the digestive tract, pancreas, rectum, lungs, or appendix. They can be non- cancerous (benign) or cancerous (malignant). They usually grow slowly over many years, but there are fast-growing forms.

There are many types of neuroendocrine tumors, but most are classified as one of two main types:

• Carcinoid tumors - NETs that most commonly arise in the digestive tract, lungs, appendix or thymus. They can also grow in the lymph nodes, brain, bone, gonads (ovaries and testes) or skin.
• Pancreatic neuroendocrine tumors (also called islet cell tumors) - NETs that typically arise in the pancreas, although they can occur outside the pancreas.

A pheochromocytoma is another, rarer type of NET that usually develops in the adrenal gland, but can also arise in other parts of the body.

Signs and symptoms depend on the tumor's type, size and location; whether it produces hormones; and whether it has spread to other parts of the body (metastasized). NETs are typically described as functional or nonfunctional. Functional NETs produce a specific set of symptoms due to the production of excess hormones, while non-functional NETs generally do not cause specific symptoms. In many cases, a person has no symptoms until the tumor spreads to the liver and/or impairs the function of an organ or system. This can make NETs very hard to diagnose.

The majority of NETs are not inherited and occur sporadically in people with no family history of NETs. However, some NETs are associated with a hereditary cancer or tumor syndrome such as multiple endocrine neoplasia type 1 (most commonly), Von Hippel-Lindau disease, tuberous sclerosis, or neurofibromatosis type 1 (NF1). Inheritance of each of these is autosomal dominant.

Treatment of NETs depends on many factors such as the tumor's type, location, aggressiveness, and hormone-producing capabilities; as well as whether it has metastasized. Management options may include surveillance, surgery to remove the tumor and/or surrounding tissue, and various non-surgical therapies to shrink the tumor, stop it from growing, or manage symptoms.