LAUSR

BACKGROUND Fibroblasts and/or collagen fibrils have not been included in previous cytologic grading schemes of canine mast cell tumors (MCTs), and their association with biological behavior is broadly debated. OBJECTIVES This study aimed to evaluate the cytologic findings of canine MCT, with emphasis on the microenvironment, and propose a novel cytologic grading system correlated with mortality and histologic grade. MATERIAL AND METHODS Cytology smears of canine cutaneous MCTs were retrospectively reviewed and compared with their histopathologic counterparts using Cohen´s Kappa test. One-year survival rates were also compared with the cytologic and histopathologic variables using Pearson´s correlation test. RESULTS From 92 first-occurrence canine cutaneous MCTs, the five features most associated with mortality were selected for a new grading system. The five features were cytoplasmic granulation, fibroblast and/or collagen fibril concentrations, and the presence of mitotic figures, multinucleation, and karyomegaly. Among concordant histopathologic and cytologic cases (ie, the same grades using both systems), mortality rates were 2.6% (1/38) for low-grade and 71.4% (10/14) for high-grade cases (P < 0.001, chi-square). For false-negative and false-positive results, mortality rates were 33% (1/3) and 45% (5/11), respectively (P = 0.707). CONCLUSIONS Unlike the Camus cytologic grading system, the present amendment excluded binucleation and included fibroblasts and/ or collagen fibrils, which in higher concentrations were associated with increased survival and a low histopathologic grade. Cytologic grading with the inclusion of fibroblast and collagen fibril concentrations correlated with survival, as did the Camus cytologic and Kiupel histopathologic grades; however, further studies are needed to confirm the prognostic value of this novel cytologic grading scheme.