Effects of Differential Distribution of Microvessel Density,Possibly Regulated by miR-374a, on Breast Cancer Prognosis

Background: The discovery that microRNAs (miRNAs) regulate proliferation, invasion and metastasis providesa principal molecular basis of tumor heterogeneity. Microvessel distribution is an important characteristic ofsolid tumors, with significant hypoxia occurring in the center of tumors with low blood flow. The distributionof miR-374a in breast tumors was examined as a factor likely to be important in breast cancer progression.
Methods: Breast tissue samples from 40 patients with breast cancer were classified into two groups: a highlyinvasive and metastatic group (HIMG) and a low-invasive and metastatic Group (LIMG). Samples were collectedfrom the center and edge of each tumor. In each group, six specimens were examined by microRNA array, andthe remaining 14 specimens were used for real-time RT-qPCR, Western blot and immunohistochemical analyses.Correlation analysis was performed for the miRNAs and target proteins. Follow-up was carried out during 28months to 68 months after surgery, and survival data were analyzed.
Results: In the LIMG, the relative contentof miR-374a was lower in the center of the tumor than at its edge; in the HIMG, it was lower at the edge of thetumor, and miR-374a levels were lower in breast cancer tissues than in normal tissues. There was no differencebetween VEGF-A and VCAM-1 mRNA levels at the edge and center of the tumor; however, we observed asignificant difference between VEGF-A and VCAM-1 protein expression levels in these two regions. There wasa negative correlation between miR-374a and target protein levels. The microvessel density (MVD) was lower inthe center of the tumor than at its edge in HIMG, but the LIMG vessels were uniformly distributed. There wasa significant positive correlation between MVD and the number of lymph node metastases (Pearson correlation,r=0.912, P<0.01). The median follow-up time was 48.5 months. LIMG had higher rate of disease-free survival(100%, P=0.013) and longer median survival time (66 months) than HIMG, which had a lower rate of 75% andshorter median survival time (54 months).
Conclusions: Our data demonstrated miR-374a to be differentiallydistributed in breast cancer; VEGF-A and VCAM-1 mRNA had coincident distribution, and the distribution ofteh respective proteins was uneven and opposite to that for the miR-374a. These data might explain the differencesin the distribution of MVD in breast cancer and variation in breast cancer prognosis.