MEN1 and multiple endocrine neoplasia type 1: Multiple endocrine neoplasia type 1 (MEN1) is an autosomal dominant disease caused by germline MEN1 mutations that leads to the development of multi-focal neoplastic endocrine lesions of the parathyroid glands, endocrine pancreas, duodenum, anterior pituitary, and, less commonly, stomach, adrenal cortex, thymus, and lungs [8–10].