Identification of molecular phenotypes in canine mammary carcinomas with clinical implications: application of the human classification.

Similarly to humans, canine mammary cancer represents a heterogeneous group in terms of morphology and biological behaviour. In the present study, we evaluated a series of canine mammary carcinomas based on a new human classification, initially based on gene expression profiling analysis. Similarly to human breast cancer, by using an immunohistochemistry surrogate panel based on five molecular markers [estrogen receptor, human epidermal growth factor receptor 2 (HER2), cytokeratin 5, p63 and P-cadherin], we were able to classify canine mammary carcinomas into four different subtypes: luminal A [estrogen receptor (ER)+/HER2-; 44.8%], luminal B (ER+/HER2+; 13.5%), basal (ER-/HER2- and a basal marker positive; 29.2%) and HER2 overexpressing tumours (ER-/HER2+; 8.3%). Luminal A-type tumours were characterised by lower grade and proliferation rate, whereas basal-type tumours were mostly high grade, high proliferative and positive for cytokeratin 5, p63 and P-cadherin. In addition, as in humans, basal subtype was significantly associated with shorter disease-free and overall survival rates, and we propose canine mammary carcinomas as a suitable natural model for the study of this particular subset of human carcinomas.