Mutagen sensitivity predicts poor overall and disease specific survival in patients with stage III non-small cell lung cancer treated with chemo/radiotherapy

Abstract

In light of the dismal outcome of current treatment and the significant treatment related toxicities in lung cancer, we urgently need markers to individualize our patient’s management. The mutagen sensitivity assay was developed to measure indirectly an individual’s DNA repair capacity to assess susceptibility to tobacco carcinogenesis. Since DNA repair capacity may also predict therapeutic effects and normal tissue repair after chemo/radiotherapy, we hypothesized that mutagen sensitivity may likewise serve as a biomarker for clinical outcome in lung cancer. Patients with lung cancer may have genetic instability unmasked by in vitro exposure of lymphocytes to a mutagen challenge such as bleomycin, a radiomimetic agent. In this study, we explored the role of bleomycin sensitivity in peripheral blood lymphocytes as a predictor of outcome in patients with inoperable stage III non-small cell lung cancer treated with definitive chemo/radiotherapy. 113 patients who were diagnosed with inoperable stage III non-small cell lung cancer at MD Anderson Cancer Center between 1995–2001 were included in this analysis. All patients received definitive radiotherapy with or without chemotherapy. Pre-treatment peripheral blood lymphocytes were collected and cultured for three days. Bleomycin was added for 5 hours and cells were arrested in mitosis using colcemid. Bleomycin sensitivity was measured by counting the mean number of chromatid breaks per cell in 50 metaphases. Patients with an average of more than 1.02 break/cell were considered to exhibit the bleomycin sensitivity phenotype. The data were analyzed using Kaplan-Meier survival function with S-plus 6.1 statistical software. The Log Rank test was used to compare different survivals. Spearman correlation test was used to analyze the correlation between bleomycin sensitivity and complications. High bleomycin sensitivity (mean chromatid break/cell >1.02, designated as bleomycin sensitive, BS) predicted poor disease specific survival (DSS) and overall survival (OS). The 6 years DSS was 27 % in patients with BS compared with 46 % in patients who didn’t exhibit the BS phenotype (p = 0.0094). The p value remained significant when adjusted (subgroup analysis) for smoking status, age (dichotomized at 60 years), radiation doses (50–55 GY, 55–65 GY, >65 GY). The 6 years OS was 19 % for patients with BS and 29 % for patients without BS (p = 0.0193). There was a trend toward worse local regional control and worse disease free survival among patients with BS (p = 0.0972 and 0.1813 respectively). There was no difference between two groups in distant metastasis free survival (p = 0.7695). To explore the predictive value of BS in treatment related complications, we analyzed the correlation between bleomycin sensitivity values with the toxicity grades of common treatment related complications including esophagitis, pneumonitis, and lung fibrosis. However, there was no significant correlation between BS and the treatment related complications when the side effects were analyzed individually or combined. BS correlated with poor overall survival and disease specific survival in these patients with stage III non-small cell lung carcinoma treated with chemo/radiotherapy. There was also a trend indicating poor local regional control and poor disease free survival with BS. There was no significant correlation between BS and treatment related complications. BS may function as a biomarker for poor clinical outcome for this group of patients. These data suggested the hypothesis that BS may indicate a genetic instability of cancer that contributes to high tumor grade, high genetic heterogeneity, and possible treatment resistance