Impact of interleukin-18 polymorphisms -607A/C and -137G/C on oral cancer occurrence and clinical progression

Background: The purpose of this study was to identify gene polymorphisms of interleukin-18 (IL-18) -607A/C and -137G/C specific to patients with oral cancer susceptibility and clinicopathological status. Methodology and Principal Findings: A total of 1,126 participants, including 559 healthy people and 567 patients with oral cancer, were recruited for this study. Allelic discrimination of -607A/C (rs1946518) and -137G/C (rs187238) polymorphisms of the IL-18 gene was assessed by a real-time PCR with the TaqMan assay. There was no significant association between IL-18 -607A/C polymorphism and oral cancer risk. However, among alcohol consumers, people with A/A homozygotes of IL-18 -607A/C polymorphism had a 2.38-fold (95% CI=1.17-4.86; p=0.01) increased risk of developing oral cancer compared with those with C/C homozygotes. The participants with G/C heterozygotes of IL-18 -137 polymorphism had a 1.64-fold (95% CI: 1.08-2.48; p=0.02) increased risk of developing oral cancer compared with those with G/G wild type homozygotes. Both sets of statistics were determined after adjusting for confounding factors. Among people who had exposure to oral cancer-related environmental risk factors such as areca, alcohol, and tobacco consumption, the adjusted odd ratios and 95% confidence intervals were increased to a 2.02-fold (95% CI=1.01-4.04; p=0.04), 4.04 (95% CI=1.65-9.87; p=0.002) and a 1.66-fold (95% CI=1.00-2.84; p=0.05) risk of developing oral cancer. However, patients with G/C alleles of IL-18 -137 were correlated with a lower clinical stage (AOR=0.59; 95% CI=0.39-0.89; p=0.01), smaller tumor size (AOR=0.56; 95% CI=0.35-0.87; p=0.01), and non-lymph node metastasis (AOR=0.51; 95% CI=0.32-0.80; p=0.003). Conclusion: IL-18 -137 G/C gene polymorphism may be a factor that increases the susceptibility to oral cancer, as well as a protective factor for oral cancer progression. The interactions of gene to oral cancer-related environmental risk factors have a synergetic effect that can further enhance oral cancer development.