Plasma Exosome miR-203a-3p is a Potential Liquid Biopsy Marker for Assessing Tumor Progression in Breast Cancer Patients.

Background: Timely detection of tumor progression in breast cancer (BC) patients is critical for therapeutic management and prognosis. Plasma exosomal miRNAs are potential liquid biopsy markers for monitoring tumor progression, but their roles in BC remain unclear. Methods: In the TCGA database, we first screened for miRNAs significantly associated with BC progression by comparing miRNA expression in para-carcinoma tissues, stage I BC tissues, and stage II-III BC tissues (n = 1026). Cox regression analyses and survival analyses were performed on candidate miRNAs to explore their prognostic value (n = 848). KEGG, GO, and PPI analyses were used to identify enriched pathways associated with cancer. Finally, the potential of candidate miRNAs as liquid biopsy markers was evaluated by sequencing and analyzing plasma exosomal miRNAs from our collection of 45 BC patients (14 in stage I, 31 in stage II-III) and 5 healthy controls, combined with qRT-PCR analysis to assess the correlation of candidate gene expression in plasma exosomes and BC tissues. Results: We found that only miR-203a-3p was progressively elevated with BC progression and was associated with poor prognosis in the TCGA dataset. Its potential target genes were enriched in pathways related to tumor progression, and the downregulation of 48 of these genes was associated with poor prognosis. More importantly, plasma exosomal miR-203a-3p was also found to gradually increase with BC progression, and its expression was positively correlated with miR-203a-3p in BC tissues. This result suggests that plasma exosomal miR-203a-3p may reflect the expression of miR-203a-3p in tumor tissues and serve as a potential liquid biopsy marker for monitoring BC progressions. Conclusion: We found for the first time that elevated miR-203a-3p was associated with BC progression and poor prognosis. Our findings suggested that plasma exosomal miR-203a-3p could hold potential as a liquid biopsy marker for evaluating BC progression in patients.