The study's purpose was to assess whether individuals who developed a second malignant neoplasm (SMN) after treatment for a first malignant neoplasm (FMN) had a lower ability to repair DNA double-strand breaks (DSBs) using a bioassay with γH2AX intensity as a surrogate endpoint. In a case-control study nested in a cohort of childhood cancer survivors, lymphoblastoid cell lines (LCLs) were established from blood samples collected from 94 cases (SMN) and 94 matched controls (FMN). LCLs were irradiated with ionizing radiation (2 and 5 Gy) and γH2AX intensities measured 1, 3, 5 and 24h post-irradiation. Differences in mean γH2AX intensity between cases and controls were compared using Kruskal-Wallis tests. Generalized linear models for repeated measures and conditional logistic regressions for SMN risk estimates were performed. The mean baseline γH2AX intensity measured without irradiation was 9.1 [95% confidence interval (95% CI): 8.5-9.7] in the LCLs from cases and 6.4 (95% CI: 6.0-6.8) from controls (P < 0.001). Markedly higher γH2AX intensity, particularly at 1 h post-irradiation, was also found in the LCLs from the cases compared with the controls for all FMNs and for different types of FMN. Chemotherapy and radiation doses received by bone marrow and thymus for FMN treatment showed a non-significant effect on γH2AX intensity. This case-control study shows that higher baseline and post-irradiation levels of DNA DSBs, as measured by γH2AX intensity, are associated with the risk of SMN in childhood cancer survivors. Further investigations in a prospective setting are warranted to confirm this association.
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