• Males with histologically confirmed adenocarcinoma of the prostate

• Confirmed HRD (Homologous recombination defect) in germline and/or somatic DNA analysis (tumour or blood), by a validated assay (see Appendix 1). Mutations in HR genes not listed in appendix 1 will be considered in literature suggests pathogenicity. A maximum of 10 uncharacterised or heterozygous mutations will be included.

• Age ≥ 18 years

• ECOG performance status ≤ 1

• Rising PSA confirmed on two sequential tests ≥1 week apart and a minimum value of 2 ug/L despite castrate levels of testosterone

• Serum testosterone \< 1.7 nmol/L and on an LHRH agent or post orchidectomy ≥ 1 year.

• Washout of ≥ 4 weeks from prior line of treatment, radiotherapy or surgery (aside from LHRH agent)

• Adequate bone marrow function (platelets \> 100 x 109/L, ANC \> 1.5 x 109/L, Hb \>100)

• Adequate liver function (ALT/AST \< 1.5 x ULN, bilirubin \< 2 x ULN)

⁃ Adequate renal function (creatinine clearance \> 50 ml/min)

⁃ Adequate cardiac function and reserve after cardiology assessment

⁃ Archived tissue sample available or willingness to undergo fresh biopsy

⁃ Willing and able to comply with all study requirements, including treatment, timing and/or nature of required assessments

⁃ Signed, written informed consent