A neuroendocrine tumor (NET) is a type of cancer that develops from cells of the neuroendocrine system. This system is made up of cells that release hormones in response to signals from the nervous system. Neuroendocrine tumors can occur anywhere in the body and can be benign (non-cancerous) or malignant (cancerous). Symptoms of NETs vary depending on the location and type of tumor, but may include abdominal pain, diarrhea, weight loss, and fatigue. Treatment options may include surgery, chemotherapy, radiation, and targeted therapy.