DNA Methylation of the Homeobox Genes PITX2 and SHOX2 Predicts Outcome in Non-small-cell Lung Cancer Patients

Biomarkers that facilitate prediction of disease progression in lung cancer patients might be clinically valuable in optimizing individualized therapy. In this study, the ability of the DNA methylation biomarkers PITX2 and SHOX2 to predict disease outcome in lung cancer patients has been evaluated. Quantitative, methylation-specific (HeavyMethyl), real-time polymerase chain reaction assays were used to measure DNA methylation of PITX2 and SHOX2 in bisulfite-converted DNA from formalin-fixed, paraffin-embedded tissues from 474 non-small-cell lung cancer patients. In univariate Cox Proportional Hazard analysis, high methylation of SHOX2 and PITX2 was a significant predictor of progression-free survival [SHOX2: n = 465, hazard ratio (HR) = 1.395 (1.130 to 1.721), P = 0.002; PITX2: n = 445, HR = 1.312 (1.059 to 1.625), P = 0.013]. Patients with low methylation of either PITX2 and/or SHOX2 (n = 319) showed a significantly higher risk of disease progression as compared with patients with higher methylation of both genes [n = 126; HR = 1.555 (1.210 to 1.999), P = 0.001]. This was particularly true for the subgroup of patients receiving no adjuvant radiotherapy or chemotherapy [n = 258, HR = 1.838 (1.252 to 2.698), P = 0.002]. In multivariate analysis, both biomarkers added significant independent prognostic information to pT, pN, pM, and grade. Another interesting finding of this study was that SHOX2 and PITX2 DNA methylation was shown to be inversely correlated with TTF1 (also known as NKX2-1) expression (PITX2: P = 0.018, SHOX2: P < 0.001). TFF1 expression was previously found to be associated with improved survival in the same patient cohort. DNA methylation of PITX2 and SHOX2 is an independent prognostic biomarker for disease progression in non-small-cell lung cancer patients.