Objective—To compare the Kiupel (2 categories) and Patnaik (3 categories) histologic grading systems for predicting the presence of metastasis at the time of initial examination in dogs with cutaneous mast cell tumors (MCTs). Design—Retrospective case series. Animals—386 client-owned dogs with cutaneous MCTs. Procedures—Medical records of dogs with newly diagnosed, histologically confirmed cutaneous MCTs that had undergone complete clinical staging were reviewed for clinical and histopathologic data. Results—All Patnaik grade 1 MCTs (n = 52) were classified as Kiupel low-grade MCTs, and all Patnaik grade 3 MCTs (43) were classified as Kiupel high-grade MCTs. Of the 291 Patnaik grade 2 MCTs, 243 (83.5%) were classified as Kiupel low-grade tumors, and 48 (16.5%) were classified as Kiupel high-grade MCTs. Dogs with Patnaik grade 3 MCTs were significantly more likely to have metastases at the time of initial examination than were dogs with grade 1 or 2 MCTs (OR, 5.46), and dogs with Kiupel high-grade MCTs were significantly more likely to have metastases than were dogs with Kiupel low-grade MCTs (OR, 2.54). However, 3 of 52 (5.8%) dogs with Patnaik grade 1 tumors, 48 of 291 (16.5%) dogs with Patnaik grade 2 tumors, and 44 of 295 (14.9%) dogs with Kiupel low-grade tumors had metastatic disease. Conclusions and Clinical Relevance—Findings indicated that in dogs with cutaneous MCTs, prognostication should not rely on histologic grade alone, regardless of grading system used, but should take into account results of clinical staging.

Canine perivascular wall tumors (cPWTs) arise from vascular mural cells and are included among soft tissue sarcomas (STSs). Most prognostic studies are performed on canine STSs as a general group and regardless of their specific histotype. The aim of this study was to identify pathological parameters and profiles with prognostic impact for cutaneous/subcutaneous cPWTs. Anatomical location, type of growth, surgical margins, and size and depth of the tumor were collected in 56 cPWTs. The association between each pair of variables was evaluated by χ² test. Multiple correspondence analysis (MCA) was performed to describe the multivariate association of variables and was followed by cluster analysis to identify specific pathological profiles. The prognostic impact of variables and profiles was assessed by Cox regression model. Size and depth were significantly associated with increased relapse probability. Cases with complete surgical margins did not recur. Other single variables were not significantly associated with relapse. Cluster analysis on MCA considering site, depth, margins, and type of growth identified 3 pathological profiles associated with PWT relapse and having a high prognostic impact. Major prognostic factors for cPWTs were tumor size, depth of growth, and pathological profiles.