<br>        Inclusion Criteria:<br><br>          1. Capable of giving signed informed consent, which includes compliance with the<br>             requirements and restrictions listed in the informed consent form and in the study<br>             protocol.<br><br>          2. Provision of signed and dated, written informed consent form prior to any mandatory<br>             study specific procedures, sampling, and analyses.<br><br>          3. For inclusion in i) the optional exploratory genetic research and ii) the optional<br>             biomarker research, patients must fulfill the following criteria:<br><br>               -  Provision of informed consent for genetic research prior to collection of sample.<br><br>               -  Provision of informed consent for biomarker research prior to collection of<br>                  sample.<br><br>             If a patient declines to participate in the optional exploratory genetic research or<br>             the optional biomarker research, there will be no penalty or loss of benefit to the<br>             patient. The patient will not be excluded from other aspects of the study.<br><br>          4. Patients must be =18 years of age (or =19 years of age in South Korea) at the time of<br>             signing the informed consent form. For patients enrolled in Japan who are <20 years of<br>             age, written informed consent should be obtained from the patient and from his legally<br>             acceptable representative.<br><br>          5. Histologically or cytologically confirmed prostate adenocarcinoma.<br><br>          6. Metastatic status defined as at least 1 documented metastatic lesion on either a bone<br>             scan or a computed tomography(CT)/ magnetic resonance imaging (MRI) scan.<br><br>          7. First-line metastatic castration-resistant prostate cancer (mCRPC).<br><br>          8. Ongoing androgen deprivation with gonadotropin-releasing hormone analogue or bilateral<br>             orchiectomy, with serum testosterone <50 nanograms per decilitre (ng/dL) (<2.0<br>             nanomoles per litre (nmol/L)) within 28 days before randomisation. Patients receiving<br>             androgen deprivation therapy (ADT) at study entry should continue to do so throughout<br>             the study.<br><br>          9. Candidate for abiraterone therapy with documented evidence of progressive disease.<br><br>         10. Patients must have normal organ and bone marrow function measured within 28 days prior<br>             to administration of study treatment.<br><br>         11. Eastern Cooperative Oncology Group (ECOG) performance status 0-1, with no<br>             deterioration over the previous 2 weeks.<br><br>         12. The participant has, in the opinion of the investigator, a life expectancy of at least<br>             6 months.<br><br>         13. Prior to randomisation, sites must confirm availability of either an archival formalin<br>             fixed, paraffin embedded (FFPE) tumour tissue sample, or a new biopsy taken during the<br>             screening window, which meets the minimum pathology and sample requirements in order<br>             to enable homologous recombination repair (HRR) status subgroup analysis of the<br>             primary endpoint radiographic progression-free survival (rPFS). If there is not<br>             written confirmation of the availability of tumour tissue prior to randomisation, the<br>             patient is not eligible for the study.<br><br>         14. Male patients must use a condom during treatment and for 3 months after the last dose<br>             of olaparib+abiraterone when having sexual intercourse with a pregnant woman or with a<br>             woman of childbearing potential. Female partners of male patients should also use a<br>             highly effective form of contraception if they are of childbearing potential.<br><br>        Exclusion Criteria:<br><br>          1. Has a known additional malignancy that has had progression or has required active<br>             treatment in the last 5 years.<br><br>          2. Patients with myelodysplastic syndrome (MDS)/ acute myeloid leukaemia (AML) or with<br>             features suggestive of yelodysplastic syndrome (MDS)/ acute myeloid leukaemia (AML).<br><br>          3. Clinically significant cardiovascular disease Association Class II-IV heart failure or<br>             cardiac ejection fraction measurement of <50% during screening as assessed by<br>             echocardiography or multigated acquisition scan.<br><br>          4. Planned or scheduled cardiac surgery or percutaneous coronary intervention procedure.<br><br>          5. Prior revascularisation procedure (significant coronary, carotid, or peripheral artery<br>             stenosis).<br><br>          6. Uncontrolled hypertension (systolic blood pressure (BP) =160 millimeters of mercury<br>             (mmHg) or diastolic blood pressure (BP) =95 millimeters of mercury (mmHg)).<br><br>          7. History of uncontrolled pituitary or adrenal dysfunction.<br><br>          8. Active infection or other medical condition that would make prednisone/prednisolone<br>             use contraindicated.<br><br>          9. Any chronic medical condition requiring a systemic dose of corticosteroid >10<br>             milligrams (mg) prednisone/prednisolone per day.<br><br>         10. Patients who are considered a poor medical risk due to a serious, uncontrolled medical<br>             disorder, non-malignant systemic disease or active, uncontrolled infection.<br><br>         11. Persistent toxicities (Common Terminology Criteria for Adverse Events [CTCAEs] grade<br>             >2) caused by previous cancer therapy, excluding alopecia.<br><br>         12. Patients with brain metastases. A scan to confirm the absence of brain metastases is<br>             not required.<br><br>         13. Patients with spinal cord compression are excluded unless they are considered to have<br>             received definitive treatment for this and have evidence of clinically stable disease<br>             for 4 weeks.<br><br>         14. Patients who are unevaluable for both bone and soft tissue progression<br><br>         15. Patients who are unable to swallow orally administered medication and patients with<br>             gastrointestinal disorders likely to interfere with absorption of the study<br>             medication.<br><br>         16. Immunocompromised patients<br><br>         17. Patients with known active hepatitis infection (ie, hepatitis B or C).<br><br>         18. Any previous treatment with Polyadenosine 5'diphosphoribose [poly (ADP ribose)]<br>             polymerase (PARP) inhibitor, including olaparib.<br><br>         19. Patients receiving any systemic chemotherapy or radiotherapy (except for palliative<br>             reasons) within 3 weeks prior to study treatment. Patients who receive palliative<br>             radiotherapy need to stop radiotherapy 1 week before randomisation.<br><br>         20. Any previous exposure to a Cytochrome P450 (CYP) 17 (17a-hydroxylase/C17,20-lyase)<br>             inhibitor (eg, abiraterone, orteronel).<br><br>         21. Concomitant use of known strong Cytochrome P450 (CYP) 3A inhibitors (eg, itraconazole,<br>             telithromycin, clarithromycin, protease inhibitors boosted with ritonavir or<br>             cobicistat, indinavir, saquinavir, nelfinavir, boceprevir, telaprevir) or moderate<br>             CYP3A inhibitors (eg, ciprofloxacin, erythromycin, diltiazem, fluconazole, verapamil).<br>             The required washout period prior to starting study treatment is 2 weeks.<br><br>         22. Concomitant use of known strong Cytochrome P450 (CYP) 3A inducers (eg, phenobarbital,<br>             enzalutamide, phenytoin, rifampicin, rifabutin, rifap