MEN1 and gastrin-producing neuroendocrine tumor: Third, in addition to the NF-pNET in MEN1 patients, 20–71% of MEN1 patients have ZES/MEN1 [290], which is primarily due to the presence of duodenal gastrinomas (85–95%) which are invariable multiple, small (<0.5 cm), and frequently metastasize to adjacent lymph nodes (40–60%) [2,288,477,480,484].