Because cytochrome P450 2A6 (CYP2A6) mediates nicotine oxidation and the metabolic activation of tobacco-related procarcinogens [6, 7], the involvement in tumor development of polymorphic CYP2A6 with impaired activities resulting from whole-gene deletion of CYP2A6 was postulated [8]. This evidence concerns the gene CYP2A6 and neoplasm.