Interestingly, there was no clear association with patients diagnosed at a younger age or those with a family history of cancer. This has great implications, not only for possible therapeutic options but for genetic and family counseling.
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One example of agents in clinical trials for patients harboring HRD are poly-ADP ribose polymerase (PARP) inhibitors. Mutations in genes that are important for the repair of double-strand DNA breaks by HRD can lead to hypersensitivity of cancer cells to PARP inhibition. This is because PARP1 repairs single strand breaks and inhibition of PARP1 in tumors with HRD are believed to lead to widespread double strand breaks that cannot be repaired, resulting in cancer cell death via so-called synthetic lethality. Early data with the PARP1 inhibitor, olaparib, showed 88% of patients with HRD to respond to the agent either by soft tissue disease response, PSA decline or circulating tumor cell count decline.  Now many trials are underway in prostate cancer, both in biomarker selected and unselected patient populations (see specific single agent trials for metastatic castration resistant prostate cancer highlighted below).
The point of this article is not only to bring awareness to our community for these exciting new clinical trials with PARP inhibitors but also to broaden awareness to the fact that these genetic alterations are common, both somatic and germline. As a result, our field needs to consider significant reaction to this by initiating efforts around the world to address these findings. As next generation sequencing becomes more frequently utilized, I believe that more high-risk prostate cancer clinics staffed with experts and genetic counselors will be needed to help address both familial and therapeutic implications of these widespread and clinically important findings. As we move forward, we must also be mindful of the fact that any agents that induce double strand breaks may lead to hypersensitivity of cells where HRD is present. This would include agents like platinum, mitoxantrone, radium-223 and others, which we will highlight in future letters from the Clinical Trials Portal.
Trials of note:
- Niraparib phase 2 NCT02854436
- Rucaparib NCT02952534
- Rucaparib vs. patient choice NCT02975934
1. Robinson D, Van Allen EM, Wu YM, et al. Integrative clinical genomics of advanced prostate cancer. Cell 2015; 161(5):1215-1228.
2. Pritchard CC, Mateo J, Walsh MF, et al. Inherited DNA-repair gene mutations in men with metastatic prostate cancer. N Engl J Med 2016; 375(5):443-453.
3. Mateo J, Carreira S, Sandhu S, et al. DNA-repair defects and olaparib in metastatic prostate cancer. N Engl J Med 2015; 373(18):1697-1708.