Aberrant methylation of the FHIT gene in chronic smokers with early stage squamous cell carcinoma of the lung

Fragile histidine triad (FHIT) gene plays an important role in the pathogenesis of lung cancer. However, the clinicopathological significance of CpG island hypermethylation of FHIT gene in non-small cell lung cancer (NSCLC) remains to be elucidated. We studied FHIT methylation in 254 NSCLCs in order to further understand the clinicopathological and prognostic significance of FHIT methylation in NSCLC. Methylation status of the FHIT gene was examined using Methylation-Specific PCR. All statistical analyses were two-sided, with a 5% type I error rate. Hypermethylation of the FHIT gene occurred more frequently in squamous cell carcinoma than adenocarcinoma. For 93 adenocarcinomas there was no statistically significant association between FHIT methylation and age, gender, smoking history, pathologic stage and p16 methylation. However, FHIT methylation in 125 squamous cell carcinomas was associated with exposure to tobacco smoke and p16 methylation, but not with age, gender and pathologic stage. Hypermethylation of FHIT in squamous cell carcinomas occurred more frequently in current smokers (45%) than in never-smokers (13%). FHIT methylation was significantly associated with p16 methylation in current- and ex-smokers (P = 0.02 and P = 0.01, respectively) with squamous cell carcinoma and in patients with pathologic stage I squamous cell carcinoma (P = 0.001). Patients with p16 methylation were 3.74 times [95% confidence interval (CI) = 1.62 - 7.95; P = 0.001] more likely to have FHIT methylation in squamous cell carcinoma. FHIT methylation in squamous cell carcinoma occurred at a 4.62 times (95% CI = 1.26 - 34.97; P = 0.02) higher prevalence in current smokers than in never-smokers. No prognostic effect of FHIT methylation was observed in stage I and stage II NSCLCs. In conclusion, hypermethylation of the FHIT gene did not have a prognostic significance in early stage NSCLCs. The FHIT methylation is associated with the p16 methylation and smoking in squamous cell carcinoma, suggesting that FHIT may cooperate with p16 for the development of squamous cell carcinoma of lung in individuals exposed to tobacco smoke.