Expression of Multidrug Resistance ATP-Binding Cassette(ABC)Transporters in Canine Mammary Tumors

Mammary neoplasms are the most common tumors in female dogs. They are usually treated using solely surgical mastectomy—which is recognized as unsatisfactory in many cases. Given this, the benefits of chemotherapy in dogs with mammary cancer need to be further explored. Some drugs that can be used for treating canines with mammary tumors may be substrates of uptake and/or efflux transporters such as the ATP-binding cassette (ABC) transporters. Unfortunately, very little is known regarding the pathobiology of such proteins in canine tumors, including mammary cancer. Accordingly, this study was designed to characterize the expression of ABC transporters P-glycoprotein, MRP1, and MRP2 and their relation with clinicopathologic factors in order to allow a better understanding of their influence in canine mammary cancer. P-glycoprotein was expressed in tumors from 55.8% of patients, while MRP1 and MRP2 were expressed in 37.2% and 39.5% of tumors, respectively. P-glycoprotein expression showed to be related with regional lymph node spread (P = 0.0038), as well as with tumor grade (P = 0.0353) and with a shorter survival (P = 0.0245). MRP1 revealed a strong association with a higher histological grade (P < 0.0001) and overall survival (P = 0.0002). Additionally, MRP1 was determined as prognostic indicator independent of lymph node status using Cox proportional-hazards regression multivariate analysis (P = 0.0216). No relations between MRP2 and clinicopathologic features were observed. We have found that P-glycoprotein and MRP1 are expressed in highly aggressive canine mammary tumors and are related with poor prognosis. Our results suggest that they may play a significant role in the course of canine mammary cancer progression and be promising candidate markers for a validation study on therapy outcome.

Snai-1 and Epithelial-Mesenchymal Transition-Related Protein Immunoexpression in Canine Mammary Carcinomas

Epithelial-mesenchymal transition (EMT) is defined as switching of polarized epithelial cells to a migratory fibroblastoid phenotype. EMT is known to be involved in the progression and metastasis of various cancers in humans, but this specific process is still little explored in the veterinary literature. The aim of this research was to evaluate the expression of EMT-related proteins in canine mammary carcinomas (CMCs). The expression of six EMT-related proteins in 94 CMCs of female dogs was evaluated by immunohistochemistry using a tissue array method. Additionally, clinicopathological characteristics were compared with the expression of EMT-related proteins. Loss of epithelial protein and/or acquisition of the expression of mesenchymal proteins were observed in CMCs. Loss of epithelial protein and/or acquisition of the expression of mesenchymal proteins were observed, particularly in tumors with evidence of stromal invasion;however, significance was only observed between the S100A4 and vascular invasion. In addition, Snai-1 nuclear immunoexpression was significantly related to E-cadherin loss. In conclusion, loss of epithelial proteins and/or the acquisition of mesenchymal proteins are associated with EMT and may have an important role in the evaluation of CMC patients. The unique immunoexpression pattern of Snai-1 could help to distinguish between an adenoma and a non-metastatic carcinoma and seems to be related to conversion of myoepithelial cells to a complete mesenchymal-like phenotype. Loss of E-cadherin and cytokeratin and change of immunoexpression pattern of Snai-1, N-cadherin, S100A4 and MMP-2 indicate the occurrence of EMT in canine mammary carcinomas and should result in an en bloc resection or a close follow-up.

Immunoexpression of Cathepsin D and S100A4 Protein and Their Molecular Subtyptes in Canine Mammary Carcinomas

Cathepsin D (CD), a lysosomal protease, and S100A4 protein, a calcium binding motif, are considered to be involved in metastasis in various human cancers. No data regarding such proteins are available for canine mammary carcinomas (CMCs). Accordingly, their expression in association with known factors of prognosis was investigated in this study. For that, 66 surgically resected CMCs were submitted to an immunohistochemical evaluation using anti CD, S100A4 protein, HER2, estrogen receptor α, cytokeratin 5, and p63 antibodies, further characterizing the tumors' molecular subtype. An increase in S100A4 immunoexpression by neoplastic luminal mammary cells was associated with an infiltrative tumor mode of growth, consequently leading us to conclude that S100A4 protein could be related to progression in CMCs. Additionally, the occurrence of the luminal A molecular subtype was associated with the complex histotype in CMCs. Although we have demonstrated that changes in S100A4 protein immunoexpression occurs in CMCs, further studies are needed to determine whether this represents important independent biomarkers for CMCs.