Abstract
MLL3 histone methyltransferase, encoded by the KMT2C gene, is a tumor suppressor that has an essential role in cell-type-specific gene expression. We evaluated the prognostic significance of KMT2C promoter methylation as a circulating epigenetic biomarker in plasma cell-free DNA (cfDNA) in non-small cell lung cancer (NSCLC). We examined the methylation status of KMT2C promoter using a novel highly specific and sensitive real-time methylation-specific PCR (MSP) assay in (a) operable NSCLC: 48 fresh-frozen NSCLC tissues, their corresponding adjacent non-neoplastic tissues, and 48 matched plasma samples; (b) metastatic NSCLC: 91 plasma samples; and (c) 60 plasma samples from healthy donors (HD). KMT2C promoter methylation in plasma cfDNA was detected in 7/48 (14.6%) patients with operable and in 18/91 (19.8%) patients with advanced NSCLC but in none (0/60, 0%) of the plasma samples from HD. In operable NSCLC, in corresponding adjacent non-neoplastic tissue samples, KMT2C promoter methylation was detected in 3/48 (6.3%) cases. Moreover, in operable NSCLC, KMT2C promoter methylation in plasma cfDNA was related to reduced disease-free survival (ΗR = 0.239; P = 0.001) and worse overall survival (OS; HR = 0.342, P = 0.023). In metastatic NSCLC, KMT2C promoter methylation in plasma cfDNA was related to worse progression-free survival (PFS; HR = 0.431; P = 0.005) and worse OS (HR = 0.306; P < 0.001). Our data strongly suggest that the detection of KMT2C promoter methylation in plasma cfDNA predicts poor prognosis in patients with both operable and metastatic NSCLCs. KMT2C promoter methylation in plasma cfDNA therefore merits further evaluation and validation as a noninvasive circulating epigenetic biomarker.