To determine whether miR-21 also regulates PDCD4 expression in prostate cancer, PC-3 and LNCaP cell lines were transfected with miR-21 inhibitor to reduce the amount of endogenous miR-21 before measuring PDCD4 mRNA and protein expression by real-time PCR and immunoblotting, respectively. This evidence concerns the gene PDCD4 and Familial prostate cancer.