['The aim of this study was to investigate the relevance of mRNA expression and DNA methylation of GST-PI in tumor and non-tumor lung tissue from NSCLC patients in terms of prognostic and pathogenetic value of this biomarker.', 'Quantitative real-time PCR was used to measure mRNA expression and DNA methylation of GST-PI in paired tumor (T) and non-tumor (N) lung tissue of 91 NSCLC patients. Of all 91 patients 49% were stage I, 21% stage II and 30% stage IIIA. Forty-seven percent of the patients had squamous cell carcinoma, 36% adenocarcinoma and 17% large cell carcinoma. All patients were R0 resected.', 'GST-PI mRNA expression could be measured in 100% in both (T and N) tissues; GST-PI DNA methylation was detected in 14% (N) and 14% (T). The median GST-PI mRNA expression in N was 7.83 (range: 0.01-19.43) and in T 13.15 (range: 0.01-116.8; p≤0.001). The median GST-PI methylation was not significantly different between T and N. No associations were seen between the mRNA expression or DNA methylation levels and clinical or histopathologic parameters such as gender, age, TNM stage, tumor histology and grading. The median survival of the investigated patients was 59.7 years (the median follow-up was 85.9 months). High GST-PI DNA methylation was significantly associated with a worse prognosis (p=0.041, log rank test). No correlation was found between the GST-PI DNA methylation levels and the correlating mRNA expression levels.'] Is glutathione S-transferase PI ( GST-PI ) mRNA expression and DNA methylation involved in the pathogenesis and prognosis of NSCLC?