The present invention relates to a method of improving the efficacy of treatment of line 2+ metastatic castration-resistant prostate cancer (mCRPC) with biallelic DNA-repair anomalies in a male human, wherein said biallelic DNA-repair anomalies are selected from: i) BRCA (BRCA1, BRCA2, or a combination thereof), ii) non-BRCA (ATM, FANCA, PALB2, CHEK2, BRIP1, HDAC2, or any combination thereof): or iii) any combination thereof; wherein the male human has received prior taxane-based chemotherapy and androgen receptor (AR)-targeted therapy; said method of improving the efficacy of treatment comprising administering to said male human a once-daily oral dosing of 300 mg niraparib.