Moreover, most parathyroid adenomas arising in MEN1 patients harbor loss of heterozygosity (LOH) of the MEN1 wild-type allele on the somatic level, thereby arguing in favor for the Knudson’s “two hit” theory in which bi-allelic inactivation of a tumor suppressor gene is needed in order for a tumor to develop [123–125]. The gene discussed is MEN1; the disease is neoplasm.