When and How to Use PARP Inhibitors in Prostate Cancer: A Systematic Review of the Literature with an Update on On-Going Trials.

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.