Molecular analysis of DNA repair gene methylation and protein expression during chemical-induced rat lung carcinogenesis

► Promoter hypermethylation of BRCA1 was only detected in three samples of infiltrating carcinoma. ► Hypermethylation of ERCC1, XRCC1, and MLH1 was found to increase gradually throughout lung carcinogenesis progression. ► BRCA1 and MLH1 protein expression decreased progressively during lung carcinogenesis, whereas ERCC1 and XRCC1 expression were only found in later stages. ► An inverse correlation between methylation status and protein expression was found for BRCA1 and MLH1.