CONTEXT: The goal of precision oncology is to use the underlying genomic 
characteristics of the patient and the cancer to select the optimal treatment at 
a given time. The recent Food and Drug Administration (FDA) approval of the 
poly(ADP-ribose) polymerase (PARP) inhibitors olaparib and rucaparib for the 
treatment of advanced prostate cancer heralds the onset of precision medicine 
for this disease.
OBJECTIVE: To discuss the emerging role that PARP inhibitors may play as a 
personalised future treatment option in patients with prostate cancer, with a 
focus on patients with metastatic castration-resistant prostate cancer (mCRPC) 
whose tumour cells harbour mutations resulting from deficient homologous 
recombination repair (HRR).
EVIDENCE ACQUISITION: To identify publications relevant to this review, a 
systematic literature search of PubMed was conducted for articles and 
proceedings of relevant major congresses, published between January 2010 and 
March 2020, reporting the use of PARP inhibitors in the treatment of cancers.
EVIDENCE SYNTHESIS: A total of 168 publications were identified, and 18 of these 
met the criteria for subsequent review. In addition, 15 phase 2 or on-going 
phase 3 (mCRPC) studies evaluating PARP inhibitors as monotherapy or in 
combination, which had not yet reported data, were identified through 
ClinicalTrials.gov. Emerging data suggest that the greatest efficacy with 
single-agent PARP inhibitors is seen in mCRPC patients with germline or somatic 
BRCA1/2 alterations (especially BRCA2 or biallelic mutations), with potential 
efficacy also observed in men with PALB2 and FANCA mutations.
CONCLUSIONS: PARP inhibitors have demonstrated efficacy in mCRPC, and similar to 
ovarian and breast cancers, the greatest effect is observed in patients with HRR 
deficiency. The PARP inhibitors olaparib and rucaparib are now FDA approved for 
mCRPC patients with HRR mutations and BRCA1/2 mutations, respectively. 
Furthermore, when PARP inhibition is combined with novel hormonal therapies, a 
treatment benefit may be observed regardless of the HRR deficiency status. Gaps 
in the knowledge and understanding around PARP inhibitor use in prostate cancer, 
including the most appropriate diagnostic testing method for identifying an HRR 
mutation, remain to be resolved.
PATIENT SUMMARY: The poly(ADP-ribose) polymerase (PARP) inhibitors olaparib and 
rucaparib are now approved by the Food and Drug Administration for the treatment 
of advanced prostate cancer. Here, we reviewed the literature and proceedings 
from meeting presentations and published papers relevant to the use of PARP 
inhibitors in the treatment of prostate cancer. Testing methods for detecting 
homologous recombination repair gene mutations, as diagnostic tools to help 
identify patients most likely to benefit from PARP inhibitor treatment, are also 
discussed.