Analysis of circulating tumor DNA identifies homologous recombination repair molecular features of Chinese breast cancer

e13006 Background: Breast cancer (BC) is the most common cancer in women world-wide. Assessments of genomic variants in circulating tumor DNA (ctDNA) have generated great enthusiasm for their potential application as clinically actionable biomarkers in the management of BC. Alterations in homologous recombination repair (HRR), are a determinant of sensitivity to platinum chemotherapy and poly (ADP-ribose) polymerase inhibitors (PARPi) in BC. However, as far as we known, most of HRR genes, except BRCA1/2, have not yet been fully understood to date. In this study, we aimed to elucidate the comprehensive HRR genetic alteration profile of breast tumors among Chinese patients by ctDNA analysis. Methods: Plasma ctDNA from 259 patients with BC were deeply sequenced via next-generation sequencing (NGS) techniques using AcornMed Biotechnology for 808 genes panel. Molecular profiles were reviewed to identify somatic and germline pathogenic mutations in the 14 HRR genes ( ATM, BRCA1, BRCA2, BRIP1, CHEK1, CHEK2, FANCA, PALB2, RAD51B, RAD51C, RAD51D, RAD54L, CDK12, and BARD1) . Results: At our institution, 259 patients underwent NGS analysis of BC specimens. The median age was 46 (range from 31 to 79). Based on the analysis of the genetic alteration profile from our cohort, at least one of the HRR genes was observed from 29.34% of the tumor samples, with BRCA1 (8.11%), BRCA2 (5.79%), RAD51C (5.02%), CDK12 (4.63%), CHEK2 (1.93%), ATM (1.16%), and BARD1 (1.16%) as the most commonly altered genes. As compared with MSKCC dataset (Table), genetic alterations detected from our cohort affected genes involved in HRR (29.34% vs. 14.03%, P＜0.0001) pathways, with statistically different genetic alteration rates. Moreover, BRCA1/2, RAD51C, CDK12 and CHEK2 mutations exhibited higher mutation rates, whereas ATM, BRIP1 and PALB2 mutations presented a lower mutation rate in Chinese patients with breast cancer (P＜0.05). Conclusions: CtDNA can characterize the mutational feature of HRR in BC. our study contributes to the understanding of the HRR pathways and specific genetic alterations harbored by Chinese patients with BC that could potentially be developed as markers of treatment response to targeted therapeutics. Ref: Razavi P, Chang MT, Xu GT, et al. The Genomic Landscape of Endocrine-Resistant Advanced Breast Cancers. Cancer Cell. 2018 Sep 10;34(3):427-438.e6. doi: 10.1016/j.ccell.2018.08.008.[Table: see text]