Abstract 5689: Effects of homologous recombination-related gene mutation subtypes on gene instability and the efficacy of platinum-containing regiments in triple-negative breast cancer
Authors: Wang Xue , Chen Yimeng , Du Feng , Yue Jian , Si Yiran , Zhao Xiaochen , Cui Lina , Zhang Bei , Bei Ting , Yuan Peng , Xu Binghe 
Published: June 2022

Background: Platinum-containing chemotherapy is treatment with high efficacy in homologous recombination (HR) deficient cancers that arise in carriers of mutations in the BRCA1/2 genes. However, previous reports have shown that TNBC patients carrying no BRCA1/2 mutations also could benefit from platinum therapy. This study aimed to explore the association between HR-related gene mutations and genomic instability, and further evaluate the effectiveness of platinum-containing chemotherapy preliminarily.

Methods: A total of 386 TNBC patients were screened from a surgical cohort (NCT01150513) and a metastatic cohort. Finally, 189 TNBC patients with clinical and tumor sequencing data availability were included, including 149 patients treated with radical surgery and adjuvant chemotherapy. All tumor samples were collected during the surgical operation and subjected to NGS for evaluating homologous recombination deficiency (HRD) score and 15 HR-related gene pathogenic or likely pathogenic mutations (including ATM, BARD1, BRCA1, BRCA2, BRIP1, CDK12, CHEK1, CHEK2, FANCL, PALB2, PPP2R2A, RAD51B, RAD51D, RAD51C, RAD54L). HRD score was an algorithmic assessment of three biomarkers of genomic instability as loss of heterozygosity, telomeric-allelic imbalance, large-scale state transitions and based on over 10,000 single-nucleotide polymorphisms in the human genome.

Results: In 189 TNBC cohort, 40 patients (21.1%) had BRCA1/2 deleterious mutations, with additional 26 patients (13.8%) carrying mutations in HR-related genes other than BRCA1/2. Compared with BRCA1/2-intact patients, those carrying BRCA1/2m displayed a significantly higher HRD score (median, 35.5 vs 20.0; P=0.02). However, patients with HRm obtained a similar HRD score with HRwt patients (median, 28.0 vs 21.0, P=0.83). TNBC patients with PALB2m (n=8) had a small trend higher HRD score compared with BRCA1/2m (median HRD score 39.0 and 35.5), and TNBC patients with RAD51 family (n=7), ATM (n=5) and other HR-related gene mutations had a numerical trend lower HRD score compared with BRCA1/2m (median HRD score 22.0, 4.0, 14.5 and 35.5). Of the 149 patients in surgical cohort, 74 received platinum-containing, and 75 underwent platinum-free adjuvant chemotherapy. We analyzed the associations between HR-related gene mutations and disease-free survival (DFS), and found that patients with RAD51Bm (n=3), RAD51Cm (n=1) or PPP2R2Am (n=1) displayed worse DFS for patients treated with adjuvant chemotherapy (P =0.012, P&lt;0.0001 or P&lt;0.0001, respectively).

Conclusions: In this study, we found that different HR-related genes mutation subtypes may exert distinct effects on genomic instability, and mutations in HR-related genes beyond the context of BRCA1/2 may serve as a biomarker for platinum-based adjuvant therapy for TNBC patients, which warrants further studies.

Citation Format: Xue Wang, Yimeng Chen, Feng Du, Jian Yue, Yiran Si, Xiaochen Zhao, Lina Cui, Bei Zhang, Ting Bei, Peng Yuan, Binghe Xu. Effects of homologous recombination-related gene mutation subtypes on gene instability and the efficacy of platinum-containing regiments in triple-negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5689.