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 statisticalindependence is uncertain.Objective: To investigate the clinical value of histological factors in the prognostication of dogs with MCTs.Animals: One hundred and ninety-sevendogs with 199 histologically diagnosed cutaneous (n = 153) and subcutaneous (n = 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-kitmutation in exons 8 and 11 and KIT localization).Methods: Retrospective cohort study identifying dogs from searching a commercial laboratory's records (January 2017–August2020). Follow-upwas collected from clinical records. Outcome measures included MCT specific survival (MSS) and recurrence.Results: Multivariable Cox proportional hazard regression identified only mitotic count > 5 (HR 10.2; 95% CI 3.2–32.8; p < 0.001)predicted poorer MSS across all MCTs. In Patnaik grade I or II and Kiupel low-gradecutaneous MCTs, only c-kitmutation inexon 11 (HR 20.8; 95% CI 1.80–224.8; p = 0.015) predicted MSS. A c-kitmutation in exon 11 (HR 10.0; 95% CI 3.0–32.9; p < 0.001),age, and histological tumor free margins < 2 mm independently predicted cutaneous and subcutaneous MCT recurrence. InPatnaik grade I or II, and Kiupel low-gradecutaneous MCTs, c-kitmutation in exon 11 (HR 23.20; 95% CI 2.3–231.3; p = 0.007)and AgNOR (HR 13.73; 95% CI 1.6–115.6; p = 0.016) predicted MCT recurrence.Conclusion and Clinical Importance: This study suggests a comparatively greater role of c-kitmutations in exon 11 andAgNOR in the prognostication of MCTs, while Ki67 appears less important