Purpose: Therapeutic decisions in breast cancer are increasingly guided by prognostic and predictive biomarkers. Non-protein-coding microRNAs (miRNAs) have recently been found to be deregulated in breast cancers and, in addition, to be correlated with several clinico-pathological features. One of the most consistently up-regulated miRNAs is miR-21. Here, we specifically searched for differentially expressed miRNAs in high-risk breast cancer patients as compared to low-risk breast cancer patients. In the same patients, we also compared miR-21 expression with the expression of its presumed target PTEN.
Methods: Both microarray and RT-qPCR techniques were used to assess miRNA expression levels in lymph node-positive and -negative human invasive ductal carcinoma tissues. Simultaneously, PTEN protein expression levels were assessed using immunohistochemistry.
Results: miR-486-5p and miR-139-5p were found to be down-regulated in patients with lymph node metastases, whereas miR-21 was found to be up-regulated in patients with a positive lymph node status. miR-21 expression levels were found to significantly correlate with tumour size (r = 0.403, p = 0.009; Spearman's rank), whereas no relation was found between miR-21 and PTEN expression levels (Kruskal-Wallis test).
Conclusion: Down-regulation of miR-486-5p and miR-139-5p, in conjunction with up-regulation of miR-21, may represent a useful signature for the identification of high-risk breast cancer patients.