PXR was originally shown to serve as a master transcriptional regulator of xenobiotic-inducible cytochrome P450 (CYP) genes [12,13], and then was found to play a role in the activation of CYP3A4 and CYP2B6, all of which belong to a gene family that plays pivotal roles in metabolic transcription of tobacco-derived carcinogens, especially PAHs, and development of lung cancer [14,15,16,17]. This evidence concerns the gene NR1I2 and lung cancer.