Abstract 3216: H2AX is a novel prognostic marker of breast cancer

Abstract INTRODUCTION: Phosphorylation of histone variant H2AX, termed gamma-H2AX, is well known for its role in DNA damage repair. On the other hand, clinical relevance of expression of H2AX in breast cancer remains to be elucidated. Previously we found that H2AX determines clonogenic cell survival under metabolic oxidative stress and cellular levels of Reactive Oxygen Species (ROS). In this study, we investigated the impact of H2AX expression on breast cancer patients' survival, as well as underlying mechanisms. METHODS: Breast cancer patients in The Cancer Genome Atlas (TCGA) dataset were classified as either high or low expression of H2AX. Overall Survival (OS) and Disease-Free Survival (DFS) as well as Gene Set Enrichment were compared between these two groups. Gene expression of each cell lines was analyzed by RNA-seq. Radiation sensitivity was quantified using cells from patient-derived xenograft (PDX). Gene expression level after neoadjuvant chemo-radio therapy was compared using publically available database (GSE25113). RESULTS: H2AX expression level is higher in triple negative breast cancers (TNBC) than non-TNBC (p<0.001) and in HER2 positive tumors than negative tumors (p=0.048) as well as advanced Stage tumors (Stage I vs Stage II/III/IV, p=0.029). H2AX high expressing tumors showed significantly worse OS (p=0.007) as well as DFS (p=0.001) and this was the case only in advanced Stage tumors (Stage I vs Stage II/III/IV, p=0.029). There were more H2AX high tumors with advancement of Stage (Stage I: 2.8%, Stage II: 5.5%, Stage III/IV 7.4%). In agreement, breast cancer cell line clones that develop metastasis expressed higher H2AX compared from their parental cells (4T1 vs 4T1.2; p<0.001, MDA-MB-231 vs LM2-4; p=0.042). Gene Set Enrichment Analysis (GSEA) demonstrated that not only DNA repair (p<0.001) and ROS related gene set (p=0.011), but also Myc target related gene sets (p=0.002) as well as UV response related gene set (p<0.001) were significantly enriched in H2AX high patients. We also demonstrated that H2AX high expressing cells from PDX showed significantly higher sensitivity to radiation therapy with higher ROS production. Indeed, tumors that demonstrated pathological completely response (pCR) after neoadjuvant chemo-radiation therapy had a trend to have higher H2AX levels compared to non-pCR tumors (p=0.093). CONCLUSIONS: Advanced Stage breast cancers that express high levels of H2AX associated with worse OS and DFS, but showed higher sensitivity to radiation. H2AX can be a prognostic biomarker for recurrent tumor that may be sensitive to radiation therapy. Citation Format: Eriko Katsuta, Mutsuko Ouchi, Toru Ouchi, Kazuaki Takabe. H2AX is a novel prognostic marker of breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3216.