Abstract
Background: Skin tumors are the most frequently diagnosed lesions, of which 7-21% are mast cell tumors (MCTs). There is a great effort to identify factors that can influence the prospective course of MCTs. Though, the histological grade is considering an important predictor helping to determine the malignancy and metastatic potential of MCTs.
Aim: In this study, an epidemiological analysis of risk factors (breed, age, sex, and anatomical site) for dogs having MCTs was evaluated considering the respective MCTs histological grade in comparison to other skin tumors.
Methods: The study included 244 dogs affected by cutaneous MCTs from a universe of 1,185 dogs diagnosed with skin tumors. A univariable analysis with Fisher exact test was performed to determine the odds ratios (ORs) with 95% confidence intervals.
Results: Boxers had a higher predisposition to Patnaik’s grade I (OR=5.9, 95% CI 2.648-13.152) and to Kiupel’s low-grade MCTs (OR=2.6, 95% CI 1.539 - 4.447). Labrador retrievers (OR=2.1, 95% CI 1.423-3.184) and pugs (OR=12.9, 95% CI 2.336-70.931) had a predisposition for Patnaik’s grade II MCTs and Kiupel’s low-grade lesions (OR=2.3, 95% CI 1.478 - 3.597; OR=17.1, 95% CI 3.093 - 94.377, respectively). French bulldogs had a higher risk to grade III MCTs (OR=7.9, 95% CI 2.381 - 26.072). Pit bulls had a predisposition to grade III MCTs and Kiupel’s high-grade tumors (OR=4.4, 95% CI 1.221 - 16.1 and OR=4.962, 95% CI 1.362 - 18.077, respectively). Bull terriers (OR=12.7, 95% CI 2.098 - 76.818) presented higher risk for having low-grade MCTs. The perigenital area and trunk exhibit a greater risk for high grading lesion (OR=6.6, 95% CI 2.679 - 16.334; OR=1.9, 95% CI 1.028 - 3.395, respectively) and the limbs had a predisposition to grade II tumor (OR=1.6, 95% CI 1.134 - 2.395). A decreased risk of having MCT was seen in older dogs (from 7-10 years and 11-18 years) compared to that in the reference group (4-6 years).
Conclusion: When comparing to canine skin tumors, this study showed a relationship between MCT histological grading and the risk factors, age, breed and topography of canine MCTs. The variations noted in the clinical presentation of MCTs amongst predisposed dog breeds reinforces the relevance of the genetic background in MCTs carcinogenesis.

Key words: Dog; Kiupel; Mast cell tumor; Patnaik; Risk;