For this study, PC3 PCa cells, which do not naturally express KLK4, were selected due to their bone metastasis origin and high aggressiveness, thereby modeling advanced prostate cancer, and importantly, propensity to develop primary tumors and bone metastases in mice, thus providing a model to test our earlier in vitro findings as described above [5,6,7,8]. This evidence concerns the gene KLK4 and prostate cancer.