Extensive staging has no prognostic value in dogs with low-risk mast cell tumors.

In canine mast cell tumors (MCTs), distant metastasis (DM) occurs infrequently. However, high-risk MCTs or tumors with certain negative prognostic factors (NPFs) are those more prone to develop metastatic disease. Accordingly, a thorough workup might not be necessary for MCTs lacking NPFs. The objective of this study was to evaluate the rate of DM and, therefore, the benefit of extensive staging in dogs presenting with and without NPFs. Furthermore, the association between the selected NPFs and DM was assessed, and factors that may have influenced outcome were evaluated. Dogs presenting with at least one NPF (Patnaik III/Kiupel high-grade, LN metastasis, rapid growth, ulceration, recurrence, high-risk location) were defined as high-risk and without as low-risk MCTs. Ninety-nine dogs were included, with 49% of MCTs in the high-risk and 51% in the low-risk group. All seven dogs with DM were identified in the high-risk group; 43% were Patnaik III/Kiupel high-grade tumors. The median survival time (MST) for this subgroup was 84 days. Patnaik III/Kiupel high-grade and rapid growth were NPFs significantly associated with DM at staging. Furthermore, a significant difference (P < .001) in MST was demonstrated between the high-risk and low-risk groups (899 days vs. not reached). NPFs significantly associated with outcome were rapid growth, presence of DM at staging, and surgical tumor excision. These results indicate that extensive staging in the absence of NPFs does not seem to be beneficial. On the other hand, by using the selected NPFs, a subset of MCTs prone to DM can be identified. This article is protected by copyright. All rights reserved.