MEN1 and multiple endocrine neoplasia type 1: Multiple endocrine neoplasia type 1 (MEN1) syndrome, a disease susceptibility to tumors driven by MEN1 deficiency mutation, is characterized by sporadic occurrence of neuroendocrine tumors in human organs.[1] Pancreatic neuroendocrine tumors (PanNETs), which are rare tumors, have a relatively low incidence and account for a small proportion of pancreatic tumors.