CDKN1B is also frequently heterozygously inactivated in small intestine neuroendocrine tumors [49, 50], in sporadic parathyroid adenomas [51] and germline inactivated in MEN4, a newly defined subtype of MEN, human autosomal dominant disorders characterized by the occurrence of spread endocrine tumors [52, 53, 54]. The gene discussed is CDKN1B; the disease is multiple endocrine neoplasia.