Clinical Value of Various Histological Factors in Cutaneous and Subcutaneous Mast Cell Tumors in 197 Dogs.

Abstract

BACKGROUND: Many histological tests have been correlated with outcome in mast cell tumors (MCTs)in dogs, but their statistical independence is uncertain. OBJECTIVE: To investigate the clinical value of histological factors in the prognostication of dogs with MCTs. ANIMALS: One hundred and ninety-seven dogs with 199 histologically diagnosed cutaneous (n&#x2009;=&#x2009;153) and subcutaneous (n&#x2009;=&#x2009;43) MCTs treated surgically in primary care practice. All had a commercial prognostic panel performed (Patnaik and Kiupel grade, mitotic count, Ki67, AgNOR, KiAg, c-kit mutation in exons 8 and 11 and KIT localization). METHODS: Retrospective cohort study identifying dogs from searching a commercial laboratory's records (January 2017-August 2020). Follow-up was collected from clinical records. Outcome measures included MCT specific survival (MSS) and recurrence. RESULTS: Multivariable Cox proportional hazard regression identified only mitotic count >&#x2009;5 (HR 10.2; 95% CI 3.2-32.8; p&#x2009;<&#x2009;0.001) predicted poorer MSS across all MCTs. In Patnaik grade I or II and Kiupel low-grade cutaneous MCTs, only c-kit mutation in exon 11 (HR 20.8; 95% CI 1.80-224.8; p&#x2009;=&#x2009;0.015) predicted MSS. A c-kit mutation in exon 11 (HR 10.0; 95% CI 3.0-32.9; p&#x2009;<&#x2009;0.001), age, and histological tumor free margins <&#x2009;2&#x2009;mm independently predicted cutaneous and subcutaneous MCT recurrence. In Patnaik grade I or II, and Kiupel low-grade cutaneous MCTs, c-kit mutation in exon 11 (HR 23.20; 95% CI 2.3-231.3; p&#x2009;=&#x2009;0.007) and AgNOR (HR 13.73; 95% CI 1.6-115.6; p&#x2009;=&#x2009;0.016) predicted MCT recurrence. CONCLUSION AND CLINICAL IMPORTANCE: This study suggests a comparatively greater role of c-kit mutations in exon 11 and AgNOR in the prognostication of MCTs, while Ki67 appears less important.