MicroRNA-21 Expression, Serum Tumor Markers, and Immunohistochemistry in Canine Mammary Tumors

Abstract Background: Canine mammary tumors (CMTs) are one of the most common malignancies in dogs and are associated with significant mortality. Serum tumor markers and non-coding microRNAs have recently gained widespread popularity in human oncology studies. We aimed to investigate the expression of microRNA-21 (miR21), changes in serum tumor markers (CEA and CA 15-3), and immunohistochemistry in CMTs diagnosed by clinical examination, radiology, and histopathology. This study enrolled 17 female dogs: 10 with mammary tumors and seven controls without tumors. Blood samples were collected to measure miR-21, CEA, and CA 15-3, and histological samples were prepared for histological grading and immunohistochemistry. Results: CA 15-3 was elevated in all animals, whereas CEA levels showed no change compared with controls. miR-21 was upregulated 12.84-fold in animals with CMT. The most frequently recorded CMT was mixed type. Myoepithelial cells were identified by P63 immunoreactivity, but not SMA. High expression of miR-21 was observed with positive vimentin immunoreactivity, indicating a mesenchymal origin of the tumor cells. Conclusion: The present study showed that miR-21 was elevated to a greater extent than CA 15-3 (12.84-fold vs. threefold). Mixed-type tumors with positive vimentin immunoreactivity showed the highest miR-21 levels. These findings support the hypothesis that miR-21 may be a more sensitive, noninvasive indicator for CMT.