Confocal laser scanning analysis of an equine oral mast cell tumor with atypical expression of tyrosine kinase receptor C-KIT.
Authors: Seeliger F, Hess O, Pröpsting M J, Naim H Y, Kleinschmidt S, Woehrmann T, Germann P G, Baumgärtner W
Journal: Veterinary pathology
Summary
# Editorial Summary Oral mast cell tumours in horses are uncommon neoplasms, yet their biological behaviour remains poorly characterised, particularly regarding receptor expression patterns that may influence prognosis and treatment selection. This case report examined a large, ulcerated mast cell tumour from the dorsal tongue of a 20-year-old mare using conventional histopathology combined with immunohistochemistry and confocal laser scanning microscopy to investigate the spatial localisation of the tyrosine kinase receptor c-KIT, a marker often associated with mast cell differentiation and malignant potential in other species. The tumour consisted of well-differentiated, tryptase-positive mast cells with numerous eosinophilic infiltrates; notably, c-KIT expression departed from the typical membrane-associated pattern, instead showing aberrant intracytoplasmic and perinuclear localisation, primarily within the Golgi apparatus. This atypical distribution suggested defective post-translational protein processing within the neoplastic cells—a finding that advanced imaging alone could definitively establish. Despite these cellular abnormalities, the tumour pursued a benign clinical course without evidence of systemic spread or poor outcomes, indicating that c-KIT mislocalisation in equine oral mast cell tumours may not carry the same prognostic weight attributed to receptor mutations in canine or feline counterparts. For practitioners, this case reinforces that morphological differentiation and detailed receptor analysis offer greater prognostic value than receptor presence alone, and highlights the importance of species-specific tumour biology when counselling on prognosis following surgical excision of equine mast cell lesions.
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Practical Takeaways
- •Oral mast cell tumors in horses can present as firm, ulcerated nodules on the tongue and may have a favorable outcome despite unusual cellular characteristics
- •Atypical KIT expression patterns do not necessarily predict aggressive behavior or poor prognosis in equine mast cell tumors
- •Confocal microscopy can reveal subcellular protein processing abnormalities that may aid in characterizing tumor biology, though clinical significance requires further investigation
Key Findings
- •20-year-old mare presented with nodular, ulcerated mast cell tumor on right dorsolateral tongue
- •Tumor showed atypical KIT receptor localization in Golgi apparatus rather than normal membrane expression, suggesting defective protein processing
- •Dense infiltrates of well-differentiated, tryptase-positive mast cells with numerous eosinophils composed the tumor
- •Case was not associated with poor prognosis despite atypical KIT expression pattern