RB1 and Familial prostate cancer: To confirm the quiescent phenotype on a molecular level, serum-deprived PC3 and DU145 prostate cancer cells were examined for expression of quiescent markers: (1) tumor suppressor gene, retinoblastoma (RB)23,47; and (2) CDK inhibitor, cyclin-dependent kinase inhibitor 1B (p27Kip1)24.