RESUMO
miRNA involvement has been observed in almost every type of cancer, including breast cancer. The etiology of abnormal expression of miRNAs in cancer is still not clearly understood. In order to obtain insight into miRNA de-regulation in breast cancer, we analyzed expression levels of five breast cancer-related miRNAs, miRNA21, miRNA155, miRNA19a, miRNA17-5p and let7a miRNA, in both malignant and neighboring non-tumoral paraffin-embedded tissues of 47 patients with invasive ductal breast cancer. The targeted miRNAs, and a reference snRNA, U6, were analyzed by real-time polymerase chain reaction. let7a Levels were significantly lower in patients with lymphatic invasion than in those without (p=0.047). miR21 was down-regulated in 93.3% of patients with necrosis [p=0.017 (Fisher's exact test (FE))], while at least one oncogenic miRNA was up-regulated in 87.3% of the patients with invasive ductal carcinoma [p=0.009 (FE)]. In addition, tumor-suppressor miRNA was down-regulated or unaltered in 65.8% of the patients with tumor grade 2 or 3 and in all with grade 1 [p=0.047 (FE)]. Based on this preliminary study, we suggest that these miRNAs, especially let7a and miRNA21, might be useful markers in follow-up of breast cancer and in prognosis.