Challenges in next generation sequencing of homology recombination repair genomic variants in prostate cancer: A nationwide survey and calibration project in China

Background: Homologous Recombination Repair (HRR) is the most reliable and important signaling pathway for repairing DNA damage. We initiated a calibration project to better understand the NGS landscape for HRR gene testing in China, provide indications for testing standardization, and guide clinical practice. Methods: A questionnaire was used to collect laboratory information, panel design for HRR gene testing, tissue sample test parameters, plasma ctDNA sample test parameters, and procedures for variant interpretation. The testing quality of the participating laboratories was further evaluated by external quality assessment (EQA), which provided 5 FFPE slices and 5 mimic ctDNA samples as standard references for evaluation. Test results and reports were collected to assess laboratory performance. Results: Our results showed that different laboratories had significant differences in sequencing platforms, library construction technologies, genes in the testing panel, detectable mutation types, probe coverage regions, sequencing parameters, variants interpretation guidelines, and positive test rates. For the EQA test, the overall pass rate was about 60%. The average accuracy for tissue samples and ctDNA samples was 79.55% and 74.13%, respectively. It is worth noting that variants in tandem repetition regions and splice sites, and those with low allele frequency were more prone to misdetection. The most common reasons for misdetection were as follows: the testing panel did not cover the genes or the whole exon and splice sites of the genes; the variants were misclassified as benign or likely benign, and the variants failed the QC criteria. Conclusions: The discrepancies observed in our survey and EQA test affect the authenticity of HRR gene test results for prostate cancer, underlining the need to establish guidelines for HRR gene testing and variant interpretation in China, and to optimize HRR gene testing in clinical practice to improve management and patient care.