Oral epithelium as a surrogate tissue for assessing smoking-induced molecular alterations in the lungs

The lungs and oral cavity of smokers are exposed to tobacco carcinogens. We hypothesized that tobacco-induced molecular alterations in the oral epithelium are similar to those in the lungs, and thus the oral epithelium may be used as a surrogate tissue for assessing alterations in the lungs. We used methylation-specific PCR to analyze promoter methylation of the p16 and FHIT genes at baseline and 3 months after intervention in 1,774 oral and bronchial brush specimens from 127 smokers enrolled in a randomized placebo-controlled chemoprevention trial. The association between methylation patterns in oral tissues and bronchial methylation indices (methylated sites / total sites per subject) was analyzed in a blinded fashion. At baseline, promoter methylation in bronchial tissue was present in 23% of samples for p16, 17% for FHIT, and 35% for p16 and FHIT; these percentages were comparable to methylation in oral tissue: 19% (p16), 15% (FHIT), and 31% (p16 and FHIT). Data from both oral and bronchial tissues were available for 125 individuals, in whom the two sites correlated strongly with respect to alterations (P < 0.0001 for both p16 and FHIT). At baseline, the mean bronchial methylation index was far higher in patients with oral tissue methylation (in either of the two genes; 39 patients) than in patients without oral tissue methylation (86 patients): 0.53 +/- 0.29 versus 0.27 + 0.26 methylation index (P < 0.0001). Similar correlations occurred at 3 months after intervention. Our results support the potential of oral epithelium as a surrogate tissue for assessing tobacco-induced molecular damage in the lungs and thus have important implications for designing future lung cancer prevention trials and for research into the risk and early detection of lung cancer.