Extracellular vesicles-derived miR-21 as a biomarker for early diagnosis and tumor activity in breast cancer subtypes.

Emerging evidence highlights the key role of microRNA (miR)-21 in cell-to-cell communication and tumorigenesis. However, limited knowledge exists on the levels and clinical meaning of miR-21 in extracellular vesicles (EVs) of patients with breast cancer (BC). We assessed EV-derived miR-21 levels in one hundred women: 30 with early BC (EBC), 30 with metastatic BC on treatment progression (MBC), 30 cancer survivors on follow-up (FU) and 10 healthy donors (HD) as age- and body mass index (BMI)-matched controls. EVs isolated from serum samples were characterized using nanoparticle tracking analysis, scanning electron microscopy and atomic force microscopy to detect their concentration, size, morphology and mechanical properties. The levels of miR-21 in EVs was evaluated using real time PCR and compared between groups (EBC, MBC and FU vs. HD) by calculating the fold change and ΔΔCt statistic. EVs size and concentration did not differ significantly among patient groups. In the EBC group, the clinical stage at diagnosis and tumor subtype did not influence miR-21 levels. The levels of miR-21 were higher in the MBC group than in the HD group (p = 0.029), mainly in those who were human epidermal growth factor receptor 2 (HER2)+ (p = 0.0005) and hormone receptor-positive (p = 0.036). In particular, in the HER2 + subgroup, the miR-21 levels were significantly higher in those with active BC (both EBC and MBC) than in HDs (p = 0.002). Our findings suggest that miR-21 may be a promising biomarker for diagnosis and tumor activity, mainly in HER2 + BC.