Triple-negative and luminal A breast tumors: differential expression of miR-18a-5p, miR-17-5p, and miR-20a-5p.

New concepts in epigenetics, microRNAs, and gene expression analysis have significantly enhanced knowledge of cancer pathogenesis over the last decade. MicroRNAs (miRNAs) are a class of non-coding RNAs that regulate gene expression by base pairing with target messenger RNAs (mRNAs), resulting in the repression of translation or the degradation of mRNA. To compare the carcinogenic process in tumors with different prognoses, we used real-time RT-PCR to evaluate the miRNA expression profiles of 24 triple-negative breast invasive ductal carcinoma, 20 luminal A breast invasive ductal carcinoma, and 13 normal breast parenchyma controls. We extracted total RNA from tissues fixed in formol and embedded in paraffin (FFPE). Results revealed the upregulation of miR-96-5p (9.35-fold; p = 0.000115), miR-182-5p (7.75-fold; p = 0.000033), miR-7-5p (6.71-fold; p = 0.015626), and miR-21-5p (6.10-fold; p = 0.000000) in tumors group. In addition, the expression of miR-125b-5p (4.49-fold; p = 0.000000) and miR-205-5p (4.36-fold; p = 0.006098) was downregulated. When the expression profiles of triple-negative and luminal A tumors were compared, there was enhanced expression of miR-17-5p (4.27-fold; p = 0.000664), miR-18a-5p (9.68-fold; p = 0.000545), and miR-20a-5 (4.07-fold; p = 0.001487) in the triple-negative tumors compared with luminal A. These data suggest that there is a similar regulation of certain miRNAs in triple-negative and luminal A tumors. However, it is possible that differences in the expression of miR-17-92 cluster will explain the phenotypic differences between these molecular tumor subtypes.