OncomiR and tumor-suppressor miR expression in triple-negative primary breast cancer.

Jelena Radojicic1, Apostolos Zaravinos2, Thomas Vrekoussis1, Maria Kafousi1, Demetrios A. Spandidos2, Efstathios N. Stathopoulos1.

1, Department of Surgical Pathology, Medical Faculty, University of Crete, 71110 Heraklion, Crete, Greece. 2, Department of Clinical Virology, University of Crete, School of Medicine, 71110 Heraklion, Crete, Greece.

Basal like-breast cancer expresses none of the three breast cancer markers (ER, PR and Her2) and is associated with a poorer prognosis since it is treated with conventional and moderately successful chemotherapies. miRNAs are small, regulatory molecules approximately 21-24 nucleotides in length. They function at the post-transcriptional level by controlling the expression of more than 50% of human protein-coding genes and play an essential role in cell signaling pathways.

Forty-nine primary triple-negative breast cancer cases, along with 34 matched tumor-associated normal samples were investigated for the expression of 9 miRNAs using qPCR. Relationships among the expression of miR-10b, miR-21, miR-122a, miR-145, miR-205, miR-210, miR-221, miR-222 and miR-296 and the pathologic features of the tumors were examined, as were as the influences of miR expression on patient overall and cancer-specific survival.

miR-21, miR-210 and miR-221 were significantly over-expressed (fold expression±SD of miR-21, 2.55±1.88, p<0.001; miR-210, 3.74 ± 4.01, p<0.001; miR-221, 1.52±1.95, p=0.0312), whereas miR-10b, miR-145, miR-205, miR-122a were significantly under-expressed in the triple-negative primary breast cancers (fold expression±SD of miR-10b, 0.36±0.36, p<0.001; miR-145, 0.30±0.39, p<0.001; miR-205, 0.80±1.37, p=0.01; miR-122, 0.017±0.05, p=0.0096). Expression of miR-222 and miR-296 did not exhibit any significant difference between the breast cancer and normal tissue. There was a non-significant trend for high expression levels of miR-210 to be associated with worse disease-free patient survival (p=0.0658).

The objective of the present study was to explore the expression profile of oncomiRs and tumor-suppressor miRs, and to define their possible correlations in triple-negative (ER, PR and Her2/neu) primary breast cancers.

Our study revealed a significant over-expression of miR-210, miR-21 and miR-221, and a significant down-regulation of miR-10b, miR-122a, miR-145 and miR-205 in triple-negative primary breast cancers. High levels of miR-21, miR-210 and miR-221, exhibited a trend to correlate with worse patient disease-free and overall survival of the patients.

Figure 1. Microphotographs (x400) of a representative breast cancer case diagnosed as triple negative: (A) Hematoxylin-Eosin staining. (B–D) Immunohistochemical detection for ER, PR and HER-2 respectively. It is obvious that this case is negative for ER, PR and HER-2 (triple negative).

Figure 2. Distribution of the normalized expression levels of nine microRNAs in breast cancer and its adjacent normal tissue. Bars indicate median values with interquartile range. C, breast cancer tissue; N, adjacent normal tissue; p < 0.05 significant.

Figure 3. Fold expression profile of microRNA data in basal breast carcinoma versus tumor-associated normal tissue. Data represent the normalized ratio of miRNA values (log2 trasformed), with upregulated and downregulated miRNAs. Vertical lines indicate standard deviation of the mean.

Figure 4. There was a non-significant trend for high expression levels of miR-210 to be associated with worse disease-free patient survival (p=0.0658).