Abstract
BACKGROUND: Molecular biomarkers assisting risk-group assignment and subsequent treatment stratification are urgently needed for patients with squamous cell cancer of the head and neck region (HNSCC). Aberrant methylation is a frequent event in cancer and, therefore, a promising source for potential biomarkers. Here, the methylation status of the paired-like homeodomain transcription factor 3 (PITX3) was evaluated in HNSCC. METHODS: Using a quantitative real-time PCR, PITX3 methylation was assessed in a cohort of 326 HNSCC patients treated for localized or locally advanced disease (training cohort). The results were validated with Infinium HumanMethylation450 BeadChip data from a 528 HNSCC patient cohort (validation cohort) generated by The Cancer Genome Atlas (TCGA) Research Network. RESULTS: PITX3 methylation was significantly higher methylated in tumor compared to normal adjacent tissue (NAT; training cohort: median methylation NAT 32.3%, tumor 71.8%, p < 0.001; validation cohort: median methylation NAT 16.9%, tumor 35.9%, p < 0.001). PITX3 methylation was also significantly correlated with lymph node status both in the training (p = 0.006) and validation (p < 0.001) cohort. PITX3 methylation was significantly higher in HPV-associated (p16-positive) tumors compared to p16-negative tumors (training cohort: 73.7 vs. 66.2%, p = 0.013; validation cohort: 40.0 vs. 33.1%, p = 0.015). Hypermethylation was significantly associated with the risk of death (training cohort: hazard ratio (HR) = 1.80, [95% confidence interval (CI) 1.20-2.69], p = 0.005; validation cohort: HR = 1.43, [95% CI 1.05-1.95], p = 0.022). In multivariate Cox analyses, PITX3 added independent prognostic information. Messenger RNA (mRNA) expression analysis revealed an inverse correlation with PITX3 methylation in the TCGA cohort. CONCLUSIONS: PITX3 DNA methylation is an independent prognostic biomarker for overall survival in patients with HNSCC and might aid in the process of risk stratification for individualized treatment.