Clinicopathologic and Immunophenotypic Characterization of Canine Cutaneous Mast Cell Tumors: Associations With Tumor Grade and the Tumor-Immune Microenvironment.

High-grade MCTs show immunosuppressive phenotype; immune profiling may aid prognostication.

This study characterized canine cutaneous mast cell tumors (MCTs) using histologic grading and immunophenotypic analysis to elucidate relationships between tumor grade and the tumor-immune microenvironment (TIME). Researchers analyzed biopsy-confirmed MCT cases using the Kiupel grading system and immunohistochemistry for multiple immune markers (CD4, CD8, CD25, CD57, MHC I, MHC II, PD-1, PD-L1) and mast cell tryptase. Demographic analysis revealed significant associations between tumor grade and patient age and sex, but not breed or anatomical location. Low-grade tumors demonstrated enhanced immune infiltration with greater CD4⁺, CD8⁺, and CD57⁺ T cell populations alongside elevated MHC I and II expression, indicating robust antigen presentation and immune activity. Conversely, high-grade tumors exhibited increased immunosuppressive markers including CD25⁺, PD-1⁺, and PD-L1⁺ expression. Correlation analyses demonstrated coordinated immune marker expression patterns in low-grade tumors but disrupted immune architecture in high-grade tumors. These findings establish distinct immunophenotypic profiles associated with MCT grade and suggest immune profiling may provide valuable prognostic information and guide therapeutic strategies in canine oncology.

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