CDKN1B and cancer: Similarly, triple mutants that are heterozygous for a p27 null allele(Nkx3.1+/− or −/−; Pten+/−; p27+/−) display enhanced prostate carcinogenesis, whereas mice that are homozygous null for p27(Nkx3.1+/− or −/−; Pten+/−; p27−/−) show inhibition of cancer progression29.