Histopathological and Immunohistochemical Analysis of Predictive and Prognostic Markers in Spontaneous Canine Mammary Cancer

The study investigates the interspecies similarities between canine and human mammary cancer in the sense of innovative predictive and prognostic tumour markers. Surgical resection specimens with diagnosed spontaneous primary mammary cancer obtained from 100 female canine patients were included in this study. Expression of carbonic anhydrase IX (CAIX) enzyme and human epidermal growth factor receptor 2 (HER2) expression was evaluated immunohistochemically. The study was completed with investigation of Ki67 expression and proliferation with marker of myogenous differentiation. Histopathological grading was performed using the Nottingham/modified Bloom-Richardson system. As in humans, our analysis of canine mammary cancer has shown that CAIX positivity in tumour cells significantly correlates with higher levels of HER2 immunoreactivity (P = 0.001), and increased tumour grade (P < 0.001). The percentage of smooth muscle actin (SMA) positive cases was significantly higher (P = 0.002) in the group of mammary carcinomas with CAIX positivity compared to the tumours that were negative. Using antibody Ki67 proliferative activity was not significantly different between mammary tumours that were CAIX positive and CAIX negative. Canine mammary gland carcinomas may, therefore, represent valuable animal models for the study of hypoxic signaling pathways involved in mammary carcinogenesis in humans. Further research investigating this possibility is required.