Warnakulasuriya and colleagues showed, for the first time, that immunoreactive CYP2E1 expression is markedly increased in the oral mucosa of squamous cell carcinoma and leukoplakia patients who have a history of chronic alcohol consumption, and that this CYP2E1 expression is closely correlated with acetaldehyde, MDA, and HNE adduct formation in oral keratinocytes [120] (Figure 3). Here, CYP2E1 is linked to squamous cell carcinoma.