Clinical and analytical validation for HRD status using targeted panel sequencing.

e17501 Background: In cancer therapy, understanding homologous recombination deficiency (HRD) is paramount, particularly due to its positive association with sensitivity to PARP inhibitor (PARPi) therapy. We propose using a targeted sequencing approach as a cost-effective and efficient alternative to the current standard of whole genome sequencing (WGS). In this study, we determine the sensitivity and clinical applications of a panel of 437 genes and over 12000 heterozygous SNP loci for evaluating HRD. Methods: HRD positivity for this assay was set at an HRD score of ≥38. To determine the limit of detection (LOD), we diluted 19 samples (4 tiers, 20 repeats each) with known HRD status. Accuracy of the assay was determined by comparing HRD status calls of 40 samples with those obtained through whole genome sequencing. Reproducibility of the assay was tested by measuring variance of HRD status for 30 samples between experimental conditions (2 operators* 3 repeats). Samples were obtained from 85 ovarian cancer (OC) patients undergoing platinum-based (Pt) chemotherapy and were profiled using our targeted sequencing assay. Results: The LOD for BRAC1/2 copy number deletions was established at a tumor purity (TP) of 30%. On the level of individual mutations, LODs range between 1.74% to 5.85% AF with a median of 2.26% AF. Repeatability analysis yields high concordance (APA= 97.83%, 95%CI= 95.34% - 99.00%; ANA= 97.73%, 95%CI= 95.13% - 98.95%), which emphasizes the precision of the assay. Comparisons against WGS based HRD scores reveal strong correlations, with Pearson coefficients of 0.975 for single sample (tumor sample only) and 0.987 for paired sample (tumor + normal sample) HRD score analysis. Through tumor profiling, we identified novel gene mutations associated with resistance to PARPi therapy in the HRD-positive population of our cohort. In the clinical setting, HRD-positive OC patients were found to experience longer progression free survival than their HRD-negative counterparts (median PFS = 18.3 vs 11.4 months, p<0.05). Upon further investigation, we observed that HRD-positive patients who did not carry pathogenic alterations on BRCA1/2 gene showed significantly longer PFS than HRD-negative patients without pathogenic BRCA1/2 alterations (median PFS = 18.5 vs 11.6 months, p<0.05). Conclusions: In summary, this targeted panel offers enhanced sensitivity, reliability, and precision in the assessment of HRD status for informed cancer therapy decisions. In practice, we showed that the targeted sequencing approach is a viable solution for determining HRD status of OC patients and can potentially serve as a predictive biomarker for treatment response. We believe that out assay emerges as a cornerstone in the advancement of personalized cancer care, and offers a sensitive, reliable, and precise approach to HRD assessment for improving patient outcomes.