For example, 100% of mice deficient in both p27Kip1 and PTEN (phosphatase and tensin homolog deleted from chromosome 10) (PTEN +/-; p27-/-) developed prostate tumors within 4-6 months vs. 50% of those with the PTEN mutation only [15-17]. The gene discussed is CDKN1B; the disease is prostate neoplasm.