MEN1 and tumor of parathyroid gland: Specifically, parathyroid tumors are the most common feature of MEN1, occurring in about 95% of patients; neuroendocrine tumors of the duodenum-pancreas (i.e., nonfunctioning tumors, gastrinomas, insulinomas, pancreatic polypeptidomas, glucagonomas, and vasoactive intestinal polypeptidomas) occur in about 80% of patients.