The methylation status and protein expression of CDH1, p16INK4A, and fragile histidine triad in nonsmall cell lung carcinoma

Abstract

Aberrant methylation of the promoter CpG island (methylation) is known as a major inactivation mechanism of tumor suppressor and tumor-related genes. In this study, the authors studied the presence of methylation by investigated the inactivation of genes and prognostic factors in patients with nonsmall cell lung carcinoma (NSCLC) by examining resection samples for the presence of methylation. Samples were obtained from 224 patients who underwent pulmonary resection for NSCLC. The authors used those samples to study methylation status with methylation-specific polymerase chain reaction analysis and to study protein expression with immunohistochemistry for 3 different genes: CDH1, p16INK4A, and fragile histidine triad (FHIT). The frequency of methylation in NSCLC was determined as 58.0% for CDH1, 21.9% for p16INK4A, and 52.2% for FHIT. The methylation of p16INK4A was observed significantly in heavy smokers compared either with nonsmokers or with patients who had smoked for <20 pack-years (P = .0420); it also was more significant in squamous cell carcinomas than in adenocarcinomas (P = .0343). FHIT methylation also was correlated significantly with lymph node metastasis (P = .0361). Patients who had tumors with both methylation and reduced expression of CDH1 had a significantly poorer prognosis compared with patients who had tumors both without methylation and with positive expression of CDH1 (P = .0259 and P = .0369, respectively; multivariate Cox analysis). For p16INK4A methylation, 63.3% of tumors showed reduced expression; whereas, in p16INK4A-unmethylated tumors, 33.7% showed reduced expression (P = .0002). However, for CDH1 and FHIT, no significant correlation was found for either methylation or reduced expression. Although protein expression was not inactivated by methylation alone, p16 expression was inactivated strongly by methylation. In addition, the analysis of methylation and expression of CDH1 played a clinically important role in treatment strategies for patients with NSCLC.