IntroductionCirculating tumour cells (CTCs) are associated with metastatic potential in a variety of human cancers. Although DNA methylation of cancer-related genes is a promising diagnostic and prognostic tool, it was rarely studied in relation to the presence of CTCs. ADAM23 gene, member of ADAM (a disintegrin and metalloproteinase domain) family, is involved in various biological events such as cell adhesion, fusion, migration, membrane protein shedding and proteolysis. The aberrant DNA methylation of ADAM23 was associated with expression silencing in breast, gastric, brain and other tumours. In our study we investigated the role of ADAM23 methylation in hematogenous spread of breast cancer (BC).Material and methodsTo detect CTCs, we analysed expression levels of KRT19, SLUG and TWIST genes in the CD45- enriched peripheral blood samples of 203 primary BC patients. The methylation levels of ADAM23 were quantified by pyrosequencing in formalin-fixed, paraffin-embedded tumour tissues. The hypermethylation cut-off was defined as mean ±2 standard deviation of DNA methylation in healthy breast tissues. Protein expression was evaluated in the same material by ImmunoReactive Score (German IRS system), based on the proportion of positive cells and the staining intensity of the nuclei or cytoplasm. A logistic regression was used to determine the effect of studied variables on presence of CTCs in peripheral blood.Results and discussionsCTC positivity (epithelial or mesenchymal markers) was identified in 23% of patients (16% mesenchymal, 9% epithelial and 2% both). ADAM23 hypermethylation (DNA methylation ≥10%) did not occur in mesenchymal CTC positive patients, while it was present in 28.8% of mesenchymal CTC negative patients (p=0.001). Among studied variables, the multivariate analysis identified low ADAM23 methylation level (p=0.004) and high ki67 proliferation index (p=0.005) as two most significant predictors of mesenchymal CTCs. It was shown recently that although ADAM23 inhibition enhanced invasion in breast cancer, it was not sufficient to trigger metastasis (Costa et al., 2015).ConclusionOur data indicate possible involvement of ADAM23 in hematogenous spread of BC cells. Better understanding of reversible epigenetic regulations hold promise for development of novel therapeutic approaches.This study was supported by the grants APVV-0076–10, APVV-16–0010, ITMS 26240220058 and VEGA grants no. 2/0092/15, 2/0102/17 and 1/0271/17.