In a prostate cancer study, Raffoul et al. found that pre-treatment with the soy isoflavones genistein, daidzein, and glycitein enhanced cell killing by radiation of PC-3 cells in vitro. The soy isoflavones achieved this result by activating apoptosis through up-regulation of Bax expression and PARP cleavage and down-regulation of Bcl-xL and survivin expression. This evidence concerns the gene PARP1 and prostate cancer.