To explore whether smoking or drinking habits showed synergistic effects for the risk of oral and pharyngeal cancer in subjects with higher susceptibility SNPs of MAO/COMT, the synergistic effects of cigarette smoking, alcohol drinking, and higher susceptibility SNPs of MAO/COMT on oral and pharyngeal cancers and OPMD were calculated by stratifying the uses of cigarette and alcohol across the susceptibility SNPs of MAO/COMT (Tables S4 and S5). Here, COMT is linked to pharynx cancer.