Background and aims: Despite limited sensitivity, the gold standard for the diagnosis of malignant cells in ascites is still cytology. The aim of this prospective proof-of-principle study was to evaluate DNA methylation as a molecular tool for the differential diagnosis of benign and malignant ascites.
Methods: A cohort of 79 patients with malignant and non-malignant ascites was prospectively enrolled. Ascites was assessed by cytopathological and laboratory examination. Cell pellets obtained by centrifugation were analyzed for differences in DNA methylation of of long interspersed nuclear element-1 (LINE-1) and microRNA-137. Quantitative determination of methylation in bisulfite-converted DNA was performed by pyrosequencing. In a subsequent stage, we compared our data to previously published data in the field following systematic review of the literature.
Results: Methylation status of studied LINE-1 and microRNA-137 could be reliably detected in all samples. Systematic evaluation revealed reliable reproducibility with satisfactory short- and long-term stability against degradation. Ascites from patients with a malignancy had a significantly higher methylation level of microRNA-137 compared with patients without tumor disease, whereas patients with peritonitis had significantly decreased methylation of microRNA-137. In contrast, differences in the measurement of the methylation status of LINE-1 could only be detected between patients with portal hypertension and a combination of malignant and infectious ascites. Inflammatory cells reflecting peritonitis correlated to DNA methylation changes.
Conclusions: Analysis of DNA methylation in ascites is technically feasible, well reproducible and may lead to identification of potential biomarkers for peritoneal carcinomatosis and other conditions. Inflammatory cells due to peritonitis may also be associated with DNA methylation changes and need to be considered in future studies. Profiling studied under standardized conditions will be needed to identify the appropriate biomarkers for differential diagnosis of ascites.