The clinical value of homologous recombination deficiency score in prostate cancer.

Abstract

e17011 Background: Aberrations in homologous recombination repair (HRR) genes serve as biomarkers for guiding the treatment decision of PARP inhibitors in prostate cancer (PCa). Homologous recombination deficiency (HRD) score which directly shows the consequence of the loss of HRR function (genomic scars) may be a more reliable biomarker for identifying patients who are sensitive to PARP inhibitors. Methods: This study involved 50 patients with PCa, including mHSPC (n = 37), mCRPC (n = 11), and locally advanced PCa (n = 2). Tumor tissue specimens were collected for targeted next-generation sequencing for 406 cancer-related genes and HRD detection. HRD score was calculated based on over 50,000 single-nucleotide polymorphisms (SNP) distributed across the human genome, incorporating three SNP-based assays: loss of heterozygosity, telomeric allelic imbalance, and large-scale state transition. All the experiments were performed in OrigiMed, a College of American Pathologists accredited and Clinical Laboratory Improvement Amendments certified laboratory. Results: The median HRD score was 34.5 (ranged from 14 to 64). With the median value as cutoff, the mutation rates of HRR were 32% (8/25) and 12% (3/25) in the high and low HRD score groups, respectively. BRCA2 mutations (P = 0.011), AR mutations (P = 0.032), RB1 mutations (P = 0.035) and altered HRR pathway (P = 0.017) were associated with high HRD scores. The mutation frequencies of AR and TP53 were significantly higher in mCRPC compared to mHSPC ( AR: 45.5% [5/11] vs 2.7% [1/37], P < 0.001; TP53: 63.6% [7/11] vs 24.3% [9/37], P = 0.027). A total of 9 patients carried HRR germline mutations (5 BRCA2, 1 BRIP1, 1 RAD50, 1 RAD51D, and 1 ATM). It was found that patients with BRCA2 germline mutations had a higher HRD score (median = 37) than those with other germline mutations ( BRIP1: 25, RAD50: 19, RAD51D: 35, ATM: 36). In the 6 patients who received HRD-related treatments (including cisplatin based chemotherapy or olaparib), 1 of the 2 patients with low HRD score had PSA progression after 251 days (the other one was lost to follow up), while no PSA progression was observed in the 4 patients with high HRD score with a median follow-up of 107 days (range: 40-274 days). A mCRPC case with high HRD score (37) and HRR wild-type who received second line docetaxel+cisplatin even achieved undetectable PSA. Another mHSPC patient with a high HRD score (37) and a BRCA2 germline mutation also had no detectable PSA after first-line docetaxel+cisplatin therapy. Conclusions: To our knowledge, this is the first study in China reporting the association of HRD score and platinum-based treatments in PCa. Our results supported the possibility that HRD score could be predictive for the efficacy of platinum-based chemotherapy.