Inclusion Criteria:

          1. Signed study informed consent form (ICF) and HIPAA authorization form

          2. Male age > 18 years

          3. Diagnosis of prostate cancer (pure small-cell histology or pure high-grade
             neuroendocrine histology are excluded; neuroendocrine differentiation is allowed)

          4. Ongoing gonadal androgen deprivation therapy with gonadotropin-releasing hormone
             (GnRH) analogues, antagonists or orchiectomy. Patients who have not had an orchiectomy
             must be maintained on effective GnRH analogue/antagonist therapy

          5. mCRPC as defined by serum testosterone < 50 ng/ml (for patients on GnRH analogues or
             antagonists) and at least one of the following:

               -  PSA level of at least 2 ng/ml that has risen on at least 2 successive occasions
                  at least 1 week apart

               -  Evaluable disease progression by modified RECIST 1.1 (Response Evaluation
                  Criteria in Solid Tumors)

               -  Progression of metastatic bone disease on bone scan, CT or MRI with > 2 new
                  lesions

          6. Prior therapy with abiraterone acetate, enzalutamide, apalutamide, or darolutamide

          7. Eastern Cooperative Oncology Group (ECOG) Performance Status of < 2 (see Appendix 3,
             ECOG Grading Scale)

          8. Results of previous standard DNA testing, or previous research testing, which confirms
             BRCA1, BRCA2, or PALB2 mutations (see Introduction, Section 2 for study design and
             previous research on targeted therapy) from primary, metastatic tumor or circulating
             tumor DNA, or pathogenic/likely pathogenic germline variant as assessed by a CLIA
             certified laboratory level assay for DNA sequencing.

          9. Patients must have normal organ and bone marrow function measured within 28 days prior
             to administration of study treatment as defined below:

               -  Hemoglobin > 10.0 g/dL

               -  Absolute neutrophil count (ANC) > 1.5 x 109/L

               -  Platelet count > 100 x 109/L

               -  Total bilirubin < 1.5 x institutional upper limit of normal (ULN)

               -  Aspartate aminotransferase (AST) (Serum Glutamic Oxaloacetic Transaminase (SGOT))
                  / Alanine aminotransferase (ALT) (Serum Glutamic Pyruvate Transaminase (SGPT)) <
                  2.5 x institutional upper limit of normal unless liver metastases are present in
                  which case, they must be < 5x ULN

               -  Patients must have creatinine clearance estimated using the Cockcroft-Gault
                  equation of >51 mL/min: Estimated creatinine clearance =(140-age [years]) x
                  weight (kg))/ (serum creatinine (mg/dL) x 72)

        Exclusion Criteria:

          1. Currently receiving active therapy for other neoplastic disorder(s)

          2. Concurrent enrollment in another clinical investigational drug or device study

          3. Histologic evidence of small cell carcinoma (morphology alone - immunohistochemical
             evidence of neuroendocrine differentiation without morphologic evidence is not
             exclusionary)

          4. Prior treatment with platinum, mitoxantrone or PARP inhibitor for castration resistant
             prostate cancer

          5. Known parenchymal brain metastasis

          6. Active or symptomatic viral hepatitis or chronic liver disease AST or ALT > 2.5 x ULN
             or total bilirubin > ULN (unless Gilbert's syndrome is the etiology of
             hyperbilirubinemia)

          7. Subjects with myelodysplastic syndrome/acute myeloid leukemia or with features
             suggestive of MDS/AML

          8. Concomitant use of known strong CYP3A inhibitors (e.g. itraconazole, telithromycin,
             clarithromycin, protease inhibitors boosted with ritonavir or cobicistat, indinavir,
             saquinavir, nelfinavir, boceprevir, telaprevir) or moderate CYP3A inhibitors (e.g.
             ciprofloxacin, erythromycin, diltiazem, fluconazole, verapamil). The required washout
             period prior to starting olaparib is 2 weeks

          9. Concomitant use of known strong (e.g. phenobarbital, enzalutamide, phenytoin,
             rifampicin, rifabutin, rifapentine, carbamazepine, nevirapine and St John's Wort) or
             moderate CYP3A inducers (e.g. bosentan, efavirenz, modafinil). The required washout
             period prior to starting olaparib is 5 weeks for phenobarbital and 3 weeks for other
             agents

         10. Subjects unable to swallow orally administered medication and subjects with
             gastrointestinal disorders likely to interfere with absorption of the study medication

         11. Clinically significant heart disease as evidenced by myocardial infarction, or
             arterial thrombotic events in the past 6 months, severe or unstable angina, or New
             York Heart Association (NYHA) Class II-IV heart disease or cardiac ejection fraction
             measurement of < 35 % at baseline

         12. Treatment with an investigational therapeutic within 30 days of Cycle-1

         13. Presence of dementia, psychiatric illness, and/or social situations limiting
             compliance with study requirements or understanding HIPAA authorization and/or giving
             of informed consent

         14. Any condition(s), medical or otherwise, which, in the opinion of the Investigators,
             would jeopardize either the patient or the integrity of the data obtained.