Among neoplastic hereditary syndromes, we will focus our attention on MEN1 and MEN4, a MEN1-like syndrome, and on familial prostate cancer (FPC), since these are the two types of hereditary syndromes in which variants of CDKN1B have been reported to be more frequent and of higher pathological significance. This evidence concerns the gene CDKN1B and Familial prostate cancer.