PDE5 expression was higher in both human and mouse prostate tumors and cell lines compared to normal...The addition of physiologically achievable concentrations of sildenafil enhanced docetaxel-induced PCa cell growth inhibition and apoptosis and reduced murine 3D tumoroid growth and in vivo tumorigenicity as compared with docetaxel alone...the combinatorial treatment of sildenafil and docetaxel may improve anticancer efficacy and reduce chemotherapy-induced side-effects among advanced PCa patients....