Neuroendocrine tumors (NETs) are a group of rare, heterogeneous neoplasms that arise from neuroendocrine cells found throughout the body. These cells have characteristics of both nerve cells and hormone-producing cells, and they release hormones into the bloodstream in response to signals from the nervous system. NETs can be benign or malignant and can occur in various organs, such as the lungs, gastrointestinal tract, and pancreas.