Impact of Histological Subtype on Survival in Canine Mammary Carcinomas: a Retrospective Analysis of 155 Cases

Canine mammary carcinoma (CMC) is the most common type of neoplasm in intact female dogs. While a previous study in Western countries validated the 2011 classification as an independent prognostic indicator in CMC, its role in CMC prognostication in Asian countries such as Korea remains unclear. In the present study, we estimate the survival rates in CMC types defined by the 2011 classification, elucidate the prognostic significance of the histological subtype and grade and that of the lymphatic invasion status in CMC, and validate the 2011 classification as an independent prognostic indicator in a large cohort of CMCs (excluding cases of multicentric CMCs). A total of 155 CMC cases retrieved from archived formalin-fixed, paraffin-embedded tissues, along with 2-year follow-up data, were retrospectively analysed. A significant association was found between the histological subtype of the 2011 classification and the tumour-specific survival. Carcinosarcoma, adenosquamous carcinoma and anaplastic carcinoma subtypes were associated with the poorest prognosis. Dogs with comedocarcinoma and solid carcinoma followed a disease course that was more aggressive than that observed in dogs with a carcinoma arising in a benign mixed tumour. Moreover, age, histological grade and lymphatic invasion status significantly correlated with tumour-specific survival in univariate analysis. In multivariate analysis, histological subtype, age and lymphatic invasion status remained independent prognostic factors for CMC.