However, we found that BPDE did not significantly change the expression levels of the DNMT3A protein, but it did slightly decrease DNMT3B protein levels (Figure 3), which is similar to a previous study showed that 24 h treatment with cigarette smoke significantly downregulated DNMT3B but just slightly induced DNMT3a expression in lung cancer cells [29]. This evidence concerns the gene DNMT3B and lung cancer.