Histopathological characterization and analysis of cell proliferation in 162 cases of canine subcutaneous mast cell tumors in Brazil

Abstract

There are limited publications about canine subcutaneous mast cell tumors (MCT). International studies have shown that subcutaneous MCT has longer survival times than cutaneous MCT, with lower recurrence and metastasis rates. In addition, subcutaneous MCT has a specific histopathological classification (circumscribed, combined, or infiltrative pattern). Our study evaluated 162 cases of subcutaneous MCT diagnosed from 2014 to 2017 in Brazil. The mean age of the animals was 8.6 years, with a predominance of females and higher incidence in dogs with mixed breed (n=40), followed by Boxer (n=20), Labrador Retriever (n=14), Golden Retriever (n=11) and Pug (n=10). Regarding histopathological characterization, the most common infiltrative pattern represented 54.3% of cases, followed by circumscribed (34.8%) and combined (11%) patterns. The mean mitotic index (MI) was 1.04, with 93.9% of cases presenting MI≤4 and 53.1% MI=0. The data found in this Brazilian study regarding subcutaneous MCT does not differ from those described in American studies, suggesting similar genetic and epidemiological factors. The evaluated proliferation indices suggest that subcutaneous MCT presents slow progression and should be evaluated as a distinct form of cutaneous MCT.