MLH1 Methylation-Based Testing in Peripheral Blood Mononuclear Cells is a Promising Biomarker for Colorectal Cancer Diagnosis and Prognosis

Background: Recent evidence has shown that peripheral blood mononuclear cells (PBMCs) can reflect the epigenetic profile of tissues they interact with, such as malignant cells. The hypermethylation of MLH1 promoter is a well-defined epigenetic alteration in the development of colorectal cancer (CRC). This is the first study aimed to assess the diagnostic and prognostic values of the methylation level of MLH1 promoter in PBMCs of patients with CRC.Method: In this case-control study, the methylation level at the promoter region of MLH1 was quantitatively analyzed in 60 CRC patients and 60 non-cancerous study participants via methylation-quantification of endonuclease-resistant DNA (MethyQESD). The receiver operating characteristic (ROC) curves were constructed and the areas under the curve were calculated to determine the diagnostic significance of MLH1 gene methylation.Results: Our data showed a significant increase in methylation of MLH1 in CRC patients compared with healthy participants (P < 0.001). Moreover, the specificity of MLH1 hypermethylation for precise diagnosis of healthy participants was 75% and its sensitivity for CRC diagnosis was 76.7%. With ROC curve analyses, we found that MLH1 promoter methylation holds a likelihood of 76.8% for distinguishing between CRC patients and healthy individuals (P > 0.001). Besides, MLH1 methylation levels was significantly increased in CRC patients with higher tumor stages, suggesting a probable correlation between an increased percentage of methylation and tumor progression (P < 0.001). However, no statistically significant association was found between methylation status of MLH1 and microsatellite instability (P > 0.05).Conclusion: Our results propose that MLH1 methylation status in PBMCs can be used as a promising diagnostic and prognostic biomarker and reliable factor for CRC screening.