MEN1 and neoplasm: Neuroendocrine tumors in MEN1 show biallelic loss of the MEN1 gene; loss of the first allele occurs at the germinal level (heterozygosity state), followed by loss of the second MEN1 allele at the somatic level (loss of heterozygosity; LOH), in target neuroendocrine cells, according to the Knudson’s “two-hit” hypothesis for conventional tumor suppressor genes [6,7].