The reason for reexpression of RAR-β2 after 24 h BPDE treatment may be because of BPDE-activated DNA repair mechanism and in our previous paper, we showed that BPDE treatment induced ATM expression, an early protein in the DNA repair pathway after esophageal cancer cells were insulted by BPDE and that ATM expression was associated with tobacco smoke exposure in esophageal cancer tissues [14,28]. This evidence concerns the gene ATM and esophageal cancer.