Neuroendocrine tumors are abnormal growths that begin in specialized cells called neuroendocrine cells. Neuroendocrine cells have traits similar to nerve cells and to hormone-producing cells.Neuroendocrine tumors are rare and can occur anywhere in the body. Most neuroendocrine tumors occur in the lungs, appendix, small intestine, rectum and pancreas.Neuroendocrine tumors can be noncancerous (benign) or cancerous (malignant).Diagnosis and treatment of neuroendocrine tumors depend on the type of tumor, its location, whether it produces excess hormones, how aggressive it is and whether it has spread to other parts of the body