To assess the safety of rucaparib in patients with biochemically recurrent non-metastatic castration-sensitive prostate cancer. To assess the proportion of patients with a 50% reduction in PSA levels (PSA50) compared to the baseline value at the time of study nrolment. To assess the proportion of patients with an undetectable PSA after initiation of PARPi therapy at 6 and 12 months. To evaluate overall survival. Here, KLK3 is linked to prostate carcinoma.