Pitfalls in MLH1 promoter methylation assessment, including POLEmut/MLH1meth endometrial adenocarcinoma
MLH1 promoter methylation status may serve as an important diagnostic, prognostic, and predictive biomarker in management of mismatch repair (MMR)-deficient cancers. A new commercial assay for detection of MLH1 promoter hyper-methylation (EntroGen), which interrogates regions C and D, was assessed for its performance characteristics. False positive results were obtained in 5/21 non-lesional cases, with signals limited to region C. Three were explained by overloaded reactions. Two unexplained cases were both muscle samples (2/6 muscle samples, one each of skeletal and smooth). The assay was 100 % concordant (52/52) for lesional samples with expected MLH1 promoter methylation status. These included two exceptional cases-one Lynch-associated, and one POLE-mutated endometrial carcinoma; thus expanding the spectrum of extreme cases, and demonstrate neither germline or somatic NGS results completely rule out MLH1 promoter methylation, and vice versa. The POLE