Inclusion Criteria:

          1. Subject capable of understanding & complying with protocol requirements & signed the
             informed consent form

          2. Minimum age 18 years

          3. Histologically confirmed adenocarcinoma of the prostate with tumour tissue available
             for molecular analyses

          4. At least one but no more than two previous taxane-based chemotherapy regimens. If
             docetaxel chemotherapy is used more than once, this will be considered as one regime.
             Patients may have had prior exposure to cabazitaxel treatment

          5. At least 28 days since the completion of prior therapy, including major surgery,
             chemotherapy & other investigational agents. Clinically relevant sequelae should have
             resolved to grade 1 or less prior to recommencing treatment. For hormonal treatment &
             radiotherapy refer to the protocol guidelines

          6. Documented prostate cancer progression as described in the protocol.

          7. Surgically or medically castrated, with testosterone levels of < 50 ng/dL (< 2.0 nM).
             If the patient is being treated with LHRH agonists this must have been initiated at
             least 4 weeks prior to Cycle 1 Day 1 & must be continued throughout the study.

          8. Eastern Cooperative Oncology Group Performance Status of 0, 1, 2

          9. Life expectancy > 12 weeks

         10. Able to swallow a whole tablet

         11. Patient & the patient's partner of childbearing potential, must agree to use medically
             accepted methods of contraception during the course of the study & for 3 months after
             the last dose of study drug

         12. Agreeable to have all the biomarker studies including the paired fresh tumour
             biopsies.

         13. CTC count of 5 cells/7.5mls blood or more at screening. Note: For Part B, CTC count >5
             cells/7.5mls blood is not mandatory if patient has measurable disease by modified
             RECIST and a lesion >2cm and PSA greater than or equal to 2ng/ml at screening.

         14. Adequate bone marrow, hepatic & renal function as defined in the protocol

         15. For Part B only, patients must have genomic defects associated with olaparib
             sensitivity identified by NGS by the central lab.

        Exclusion Criteria:

          1. Surgery, or local prostatic intervention (excluding a prostatic biopsy) less than 28
             days of Cycle 1 Day 1

          2. Less than 28 days from any active anticancer therapy or investigational agents. For
             hormonal treatment & radiotherapy refer to the guidelines outlined in the inclusion
             criteria

          3. Prior treatment with a PARP inhibitor, platinum, cyclophosphamide or mitoxantrone
             chemotherapy

          4. Uncontrolled intercurrent illness including, but not limited to, active infection,
             symptomatic congestive heart failure (New York Heart Association Class III or IV heart
             disease), unstable angina pectoris, cardiac arrhythmia, uncontrolled hypertension or
             psychiatric illness/social situations that would limit compliance with study
             requirements

          5. Any acute toxicities due to prior chemotherapy & / or radiotherapy that have not
             resolved to a NCI-CTCAE v4.02 grade 0 or 1 with the exception of chemotherapy induced
             alopecia & grade 2 peripheral neuropathy

          6. Malignancy within the previous 2-years with a > 30% probability of recurrence within
             12 months with the exception of non-melanoma skin cancer, in-situ or superficial
             bladder cancer

          7. Patients with myelodysplastic syndrome/acute myeloid leukaemia

          8. Patients with known symptomatic brain metastasis are not suitable for enrollment.
             Patients with asymptomatic, stable, treated brain metastases are eligible for study
             entry

          9. Patients with symptomatic or impending cord compression unless appropriately treated
             beforehand & clinically stable & asymptomatic

         10. Patients who have experienced a seizure or seizures within 6 months of study treatment
             or who are currently being treated with cytochrome P450 enzyme inducing anti-epileptic
             drugs for seizures

         11. Patients receiving any of the following classes of inhibitors of CYP3A4 (see protocol
             for guidelines & wash out periods)

         12. Patients with gastrointestinal disorders likely to interfere with absorption of the
             study medication

         13. Initiating bisphosphonate therapy or adjusting bisphosphonate dose/regimen within 30
             days prior to Cycle 1 Day 1. Patients on a stable bisphosphonate regimen are eligible
             & may continue

         14. Presence of a condition or situation, which, may put the patient at significant risk,
             confound the study results, or interfere significantly with participation in the study