Differential Frequencies of p16INK4a Promoter Hypermethylation, p53 Mutation, and K-ras Mutation in Exfoliative Material Mark the Development of Lung Cancer in Symptomatic Chronic Smokers

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Abstract
PURPOSE: The aim of this study was to investigate the frequency of three (epi)genetic alterations (p53 and K-ras mutations and p16INK4a promoter hypermethylation) in symptomatic chronic smokers compared with patients with lung cancer and to evaluate the use of exfoliative material for such analyses. PATIENTS AND METHODS: Fifty-one patients with histologically confirmed lung cancer and 25 chronic smokers (> 20 pack-years) were investigated for mutations in the K-ras (codon 12) and p53 (codons 248, 249, and 273) genes and for allelic hypermethylation of the p16INK4a gene. DNA was isolated from sputum and bilateral bronchial lavage, and brushings were taken at bronchoscopy. RESULTS: Forty-one genetic lesions were detected within exfoliative material from the group of 51 patients with lung cancer and 10 lesions in the chronic smoker group. K-ras mutations occurred exclusively in the lung cancer group, whereas p53 mutations and p16INK4a promoter hypermethylation were also found in chronic smokers. Three of eight chronic smokers who harbored an (epi)genetic alteration were subsequently diagnosed with lung cancer. Analysis of sputum yielded information equivalent to that of samples obtained during bronchoscopy. CONCLUSION: p16INK4a promoter hypermethylation and p53 mutations can occur in chronic smokers before any clinical evidence of neoplasia and may be indicative of an increased risk of developing lung cancer or of early disease. K-ras mutations occur exclusively in the presence of clinically detectable neoplastic transformation. Molecular analysis of sputum for such markers may provide an effective means of screening chronic smokers to enable earlier detection and therapeutic intervention of lung cancer.