Exosomes deep sequencing identifies miR-363-5p as a non-invasive biomarker of axillary lymph node metastasis and prognosis in breast cancer

Background: Breast cancer is the most common malignant tumor in females. Axillary lymph node (ALN) metastasis is an independent risk factor of prognosis and correlates with distant metastasis. However, the false-negative rate and complications of the standard procedure are not neglectable hitherto. It is necessary to develop an accurate non-invasive approach for lymph node staging.Methods: In this study, circulating exosomal miRNA profiles in peripheral blood from 10 patients with breast cancer and 10 age-matched healthy women were obtained and analyzed using small RNA deep sequencing. Integrative profiles analysis and multiple cross-validation using in-house and external independent datasets were performed to evaluate the diagnostic performance. Functional assays were used to analyze cellular phenotypes and downstream targets of miR-363-5p.Results: We found that the aberrant expression of exosomal miR-363-5p is significantly associated with tumorigenesis (p=0.047) and ALN metastasis (p=0.019). Serum exosomal miR-363-5p demonstrated the consistent down-regulated expression pattern in LN positive patients compared with LN negative patients across multiple independent datasets, which achieved high diagnostic performance in predicting lymph node metastasis (AUC=0.621-0.958). Furthermore, patients with a high expression level of miR-363-5p had significantly improved overall survival (HR=0.63, ±95% CI=0.45-0.89, p=0.0075). Functional experiments discovered that miR-363-5p acts by inhibiting the migration ability of breast cancer cells. Here we further identified Platelet Derived Growth Factor Subunit B (PDGFB) as a downstream target of miR-363-5p.Conclusions: The miR-363-5p deficiency promoted metastasis via facilitating PDGFB expression, leading to overactivity of PDGF signaling in cancer cells. These results demonstrated that tumor metastasis is mediated by tumor-derived exosomes that affect cell growth signal regulation. Therefore, exosomal miR-363-5p may serve as a marker for ALN metastasis diagnosis in a non-invasive manner.