BARCODE 2 is a single arm, single site phase II study with the aim to determine the response rate to two cycles of platinum chemotherapy in patients with mCRPC and a germline mutation in a DNA repair gene. Response will be measured with prostate specific antigen (PSA) levels and radiological assessment. The study will be divided into two parts. In part 1 of the study, enrolled patients' DNA repair gene mutation carrier status will be assessed using a gene panel. Men who are found to carry a pathogenic mutation or are already known to carry a germline mutation can enrol in part 2 of the study and be offered treatment with carboplatin.