CDKN2A/p16 Exon 2 Hypermethylation in Lung Squamous Cell Carcinoma Associated with Interstitial and Emphysematous Lung Diseases: A Comparative Analysis of Tumor, Adjacent and Distant Lung Tissues

Lung squamous cell carcinoma (LUSC) tends to arise in the setting of interstitial or emphysematous lung diseases, including idiopathic pulmonary fibrosis (IPF), pulmonary emphysema (PE), and smoking-related interstitial fibrosis (SRIF), where field cancerization may extend. DNA methylation of promoter regions of p16, CDH13, and RASSF1A and p16 exon 2 was assessed by methylation-specific PCR. Tumor, adjacent (<3 cm), and distant (≥3 cm) lung tissues were obtained from 25 patients with LUSC (IPF, n = 7; PE, n = 8; SRIF, n = 10). p16 exon 2 methylation was significantly higher in tumors than in non-tumorous tissues in PE and SRIF cases. In contrast, IPF cases showed p16 exon 2 hypermethylation also in distant tissues. Across tumor samples, p16 promoter hypermethylation was frequently observed in stage II or higher. p16 expression in tumors was generally reduced in IPF and PE cases, compared with SRIF cases. No consistent methylation or expression patterns were observed for CDH13 or RASSF1A. p16-associated molecular alterations exhibited disease- and stage-related differences, suggesting heterogeneity in LUSC carcinogenesis. These findings indicate a broader epigenetic field effect, as reflected by p16 exon 2, in IPF-associated LUSC and suggest that complex, elusive mechanisms underlying p16 aberrations may contribute to this phenomenon.