SMAD4 and gastrin-producing neuroendocrine tumor: SMAD4/DPC4, a putative tumor suppressor in pancreatic carcinoma, was mutated or deleted in 55% (5 of 9) of non-functioning pNETs but remained intact in 100% of the less aggressive, functional pNETs (insulinomas, gastrinomas, and VIPnomas) [276].