Abstract P3-11-06: HRD (homologous recombination deficiency) score and its clinicopathological features in neoadjuvant chemotherapy treated sporadic breast cancers

Abstract

Abstract [Purpose]Homologous Recombination Deficiency (HRD) score has been developed to evaluate the DNA double-strand break repair function. BRCA1/2 germline mutation-associated breast cancers are known to show a high HRD score and a high sensitivity to platinum-based chemotherapy as well as PARP inhibitor. HRD can be theoretically induced by not only the dysfunction of BRA1/2 but also the dysfunction of the other molecules involved in homologous recombination, and, actually, high HRD score is reported to be seen in a significant proportion of sporadic breast tumors without BRCA1/2 mutation. The aim of the present study was to elucidate the clinicopathological characteristics of sporadic breast tumors with high HRD score as well as their sensitivity to sequential paclitaxel and FEC chemotherapy (P-FEC). [Methods]Tumor tissues obtained by Mammotome from 132 sporadic breast cancer patients (stage II-III) before neoadjuvant chemotherapy with P-FEC were subjected to assay for HRD score using Oncoscan CNV kit®. HRD score was a simple sum of NtAI, LOH, and LST (cutoff, 42), and were also subjected to the gene expression analysis using the Affymetrix microarray (U133 plus 2.0). BRCA1 promoter methylation was assayed by methylation specific real-time PCR. [Result]Of the 132 breast tumors, 32% showed a high HRD score which were significantly associated with high histological grade (P=0.001), negative progesterone receptor (P=0.023) and high Ki67 index (P=0.004). Triple negative breast cancer (TNBC)(n=19) showed a significantly (P<0.001) higher HRD score than the other subtypes (HR+/HER2-(n=73), HR+/HER2+(n=12), HR-/HER2+(n=18)). BRCA1 promoter methylation was significantly associated with a high HRD score. There was no significant correlation between HRD score and pCR to P-FEC when all tumors were considered but tumors with a high HRD score showed a significantly (P=0.020) lower pCR rate when only TNBC were considered. In TNBC, majority of tumors showed a high HRD score in five subtypes (BL1, BL2, IM, M, MSL) but no tumor showed a high HRD score in LAR (luminal androgen receptor) subtype. [Conclusion]Approximately one third of sporadic breast tumors show a high HRD score, indicating the presence of homologous recombination dysfunction, and they are most often seen in TNBC with BRCA1 promoter methylation and never in LAR subtype. Interestingly, breast tumors with a high HRD score were less sensitive to P-FEC. Citation Format: Imanishi S, Naoi Y, Shimazu K, Shimoda M, Kagara N, Tanei T, Miyake T, Kim SJ, Noguchi S. HRD (homologous recombination deficiency) score and its clinicopathological features in neoadjuvant chemotherapy treated sporadic breast cancers [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P3-11-06.