Patients with MEN1 usually develop parathyroid adenomas and primary HPT (90%–100% of cases), GEP–NET which are usually multiple and located in the pancreas and duodenum, and can either be functional (gastrinoma is the most common) or nonfunctional (80%–100%), and anterior pituitary adenomas (20%–60%). Here, MEN1 is linked to gastrin-producing neuroendocrine tumor.