Constitutive expression of γ-H2AX has prognostic relevance in triple negative breast cancer
Background and purpose: Constitutive γ-H2AX expression might indicate disruption of the DNA damage repair pathway, genomic instability, or shortened telomeric ends. Here, we quantified expression of endogenous γ-H2AX and its downstream factor 53BP1 in a large number of breast cancer cell lines (n = 54) and a node-negative breast cancer cohort that had not received adjuvant systemic treatment (n = 122). Materials and methods: Formalin fixed paraffin embedded breast cancer cell lines and tumors were immunohistochemically analyzed for γ-H2AX and 53BP1 expression, and related to cell line, patient and tumor characteristics and to disease progression. Results: In breast cancer cell lines, γ-H2AX positivity was associated with the triple negative/basal like subgroup (p = 0.005), and with BRCA1 (p = 0.011) or p53 (p = 0.053) mutations. Specifically in triple negative breast cancer patients a high number of γ-H2AX foci indicated a significantly worse prognosis (p = 0.006 for triple negative vs. p = 0.417 for estrogen receptor (ER), progesterone receptor (PR) or HER2 positive patients). A similar association with disease progression was found for 53BP1. In a multivariate analysis with tumor size, grade, and triple negativity, only the interaction between triple negativity and γ-H2AX remained significant (p = 0.002, Hazard Ratio = 6.77, 95% CI = 2.07-22.2). Conclusions: Constitutive γ-H2AX and 53BP1 staining reveals a subset of patients with triple negative breast tumors that have a significantly poorer prognosis.