In the stratified analysis by tumor type, the risk of oral leukoplakia was significant associated with rs13181 polymorphism (AC vs. AA: OR = 1.28, 95% CI = 1.01-1.62, P = 0.546 for heterogeneity, I² = 0.0%; CC vs. AA: OR = 1.94, 95% CI = 0.99-3.79, P = 0.057 for heterogeneity, I² = 60.1%; dominant model AC + CC vs. AA: OR = 1.35, 95% CI = 1.08-1.69, P = 0.303 for heterogeneity, I² = 17.6%; allele C vs. A: OR = 1.38, 95% CI = 1.04-1.82.
GSTT1 null and rs1695 were inversely associated with oral leukoplakia while GSTM1 null, GSTT1 null, rs2031920, rs3813867 (CYP2E1), and rs13181 were associated with OC.