γ-H2AX expression detected by immunohistochemistry correlates with prognosis in early operable non-small cell lung cancer

BACKGROUND Phosphorylation of the H2AX histone is an early indicator of DNA double-strand breaks and of the resulting DNA damage response. In the present study, we assessed the expression and prognostic significance of γ-H2AX in a cohort of 96 patients with operable non-small cell lung carcinoma. METHODS Ninety-six paraffin-embedded specimens of non-small cell lung cancer patients were examined. All patients underwent radical thoracic surgery of primary tumor (lobectomy or pneumonectomy) and regional lymph node dissection. γ-H2AX expression was assessed by standard immunohistochemistry. Follow-up was available for all patients; mean duration of follow-up was 27.50 ± 14.07 months (range 0.2-57 months, median 24 months). RESULTS Sixty-three patients (65.2%) died during the follow-up period. The mean survival time was 32.2 ± 1.9 months (95% confidence interval [CI]: 28.5-35.8 months; median 30.0 months); 1-, 2- and 3-year survival rates were 86.5% ± 3.5%, 57.3% ± 5.1%, and 37.1% ± 5.4%, respectively. Low γ-H2AX expression was associated with a significantly better survival as compared with those having high γ-H2AX expression (35.3 months for low γ-H2AX expression versus 23.2 months for high γ-H2AX expression, P = 0.009; hazard ratio [HR] 1.95, 95% CI: 1.15-3.30). Further investigation with multivariate Cox proportional hazards regression analysis revealed that high expression of γ-H2AX remained an independent prognostic factor of shorter overall survival (HR 2.15, 95% CI: 1.22-3.79, P = 0.026). A combined p53/γ-H2AX analysis was performed, and we found that the p53 low/γ-H2AX low phenotype was associated with significantly better survival compared with all other phenotypes. CONCLUSION Our study is the first to demonstrate that expression of γ-H2AX detected by immunohistochemistry may represent an independent prognostic indicator of overall survival in patients with non-small cell lung cancer. Further studies are needed to confirm our results.