GEP NE tumors often do not produce symptoms in the early stages of disease. When symptoms do appear, they usually are caused by the higher than normal amounts of a particular hormone, or hormones, produced by the tumor cell. The effects of the tumor vary depending on the type of hormone being overproduced.

Carcinoid tumors can secrete too much of the hormone serotonin. High amounts of serotonin, as well as other less well characterized substances in the blood, can cause carcinoid syndrome, which includes:

• A red flushing of the face and neck
• Diarrhea
• Less commonly, asthma-like wheezing.

Heart valve disease and other cardiac disturbances can also occur in patients who have had carcinoid syndrome for many years. Carcinoid syndrome usually occurs when carcinoid tumors have spread to other parts of the body. When tumors have spread, they are said to have metastasized. The syndrome generally occurs in patients with metastatic small bowel or appendiceal carcinoids, and rarely, if ever, occurs in patients with metastatic bronchial or rectal carcinoid tumors.

Insulinomas secrete large amounts of the hormone insulin. High levels of insulin can cause low blood sugar, which in turn causes:

• Visual disturbances
• Weakness
• Sweating
• Confusion
• Less commonly, seizures.

Symptoms often occur early in the morning or at night, when blood sugar levels are lowest.

Gastrinomas release high amounts of gastrin, which causes hypersecretion of acid in the stomach. This can cause:

• Abdominal pain
• Diarrhea
• The development of peptic ulcers, a syndrome also known as Zollinger-Ellison syndrome.

VIPomas secrete a hormone called vasoactive intestinal peptide (VIP). Patients with VIPomas may have Verner-Morrison syndrome, which is characterized by profound secretory diarrhea.

Glucagonomas secrete high amounts of the hormone glucagon. Glucagon causes high blood sugar levels and diabetes. Patients with glucagonomas may develop a rash, called necrolytic migratory erythema. This occurs on the lower trunk, buttocks, perineum, and thighs. A dermatologist can diagnose it. Patients may also lose weight.

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