Relationship of the Levels of microRNA Gene Methylation with the Level of Their Expression and Pathomorphological Characteristics of Breast Cancer.

We studied the relationship of the levels of microRNA group expression and methylation with clinical and pathomorphological parameters of breast cancer and its immunohistochemical status. Quantitative methylation specific PCR analysis showed a significant (p<0.001) increase in the methylation level of 4 microRNA genes (MIR127, MIR129-2, MIR132, and MIR148A) and a significant (p<0.001) decrease for gene MIR375 relative to paired histologically normal tissue. Real-time PCR analysis revealed a significant (p≤0.001) decrease in the expression of 4 microRNAs (miR-127-5p, miR-129-5p, miR-132-3p, and miR-148a-3p) and a significant (p≤0.001) increase in the expression of miR-375-3p. A significant (rs=-0.6--0.7, p≤0.001) relationship between changes in the expression level of miR-129-5p, miR-132-3p, miR-148a-3p, and miR-375-3p and the levels of methylation of the corresponding genes in breast cancer was showed by using Spearman's rank correlation test. Analysis of the samples with consideration of the pathophysiological characteristics of the tumor revealed two significant markers of tumor progression: MIR129-2/miR-129-5p and MIR375/miR-375-3p. Both factors, the increase in the level of MIR129-2 methylation (p<0.001) and a decrease in the expression level of miR-129-5p (p<0.001), are significantly associated (p<0.001) with stage III/IV and the absence of HER2 expression. For MIR375/miR-375-3p, on the contrary, an association of low methylation level and enhanced expression with increased Ki-67 level (>30%, p<0.05) was revealed. These findings are of interest for understanding the mechanisms of breast cancer development and can provide the basis for the diagnosis and prognosis of the course of this disease. Moreover, the revealed features can be useful for adjusting the course of treatment with consideration of the pathophysiological characteristics of the tumor.