Association between histopathological grading, immunohistochemical markers and prognosis in canine cutaneous mast cell tumor

This study aimed to evaluate the association between biologic behavior and survival time of dogs with cutaneous mast cell tumor (MCT) with prognostic indicators. This prospective and longitudinal study followed 37 dogs with MCT. We correlated clinical factors (age, gender, time of onset, number of lesions, ulceration, tumor size, lymph node and distant metastasis, recurrence rate, and survival time) with histologic grading, immunohistochemical staining for Ki67 (samples were classified as > 23 or ≤ 23 cells positive cells/5 high-power fields) and tyrosine-protein kinase KIT pattern (cytoplasmic or membranous). The comparison between clinical data and prognostic factors was assessed individually for each variable. Multivariate analysis by logistic regression compared variables to outcome. The survival functions were calculated using the Kaplan-Meier method. There was a significant correlation between high-grade MCT and occurrence of lymph node and distant metastasis and recurrence (p < 0.05). Recurrence was also correlated with grade II and III MCTs (p = 0.03). Kappa coefficient revealed considerable agreement with significant correlation between Ki67 and KIT (p = 0.03). There was no significant association between Ki67 or KIT pattern and histologic grading or survival time. The mean overall survival time of dogs with high-grade tumors was 279 days and significantly shorter than those with low-grade (406 days) (p = 0.03). This study suggests that two-tier histologic grading is a reliable prognostic factor for dogs with MCT. KIT pattern and Ki67 index may act in association with histologic grade for the screening of these patients.