MTNR1A and lip and oral cavity carcinoma: Among betel-nut consumers in our cohort, subjects with MTNR1A polymorphic rs2119882, rs13140012, or rs6553010 genes and who smoked had corresponding 9.48- (95% CI: 2.58~34.79), 8.37- (95% CI: 1.84~38.01), and 5.33-fold (95% CI: 1.17~22.28) higher risks of having oral cancer compared to betel-quid chewers with the WT gene who did not smoke (Table 4).