Hung et al. performed a case-control study looking for the interactions between oral cancer risk factors (cigarette smoking, alcohol drinking, and betel quid chewing) and genetic polymorphisms of CYP2E1, and they found that the c1/c2 and c2/c2 genotypes were associated with an increased oral cancer risk compared to the c1/c1 genotype among the subjects who did not chew betel quid, but not among chewers [89]. The gene discussed is CYP2E1; the disease is lip and oral cavity carcinoma.