CYP2E1 and lip and oral cavity carcinoma: In terms of the cytochrome p450 (CYP) metabolism pathway, the polymorphisms of CYP-involved genes (e.g., CYP26B1, CYP1A1, CYP2A6, and CYP2E1) have been found to activate areca nut (AN)-derived nitrosamines, thereby significantly increasing the susceptibility to tobacco-induced oral cancer (Lin et al., 2013).