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Malignant mast cell neoplasia with local metastasis in a horse
1Rural Veterinary Centre, Department of Animal Health, University of Sydney, Werombi Road, Camden, New South Wales 2570, Australia.
Insights
A rare case of equine mast cell neoplasia in a stallion presented with limb swelling and lameness. This study details the unusual co-occurrence of eosinophilia with this rare cancer in horses.
Area of Science:
- Veterinary Pathology
- Equine Oncology
- Comparative Pathology
Background:
- Malignant mast cell neoplasia is uncommon in horses.
- Metastasis of equine mast cell tumors is exceptionally rare.
- Eosinophilia is a known finding in canine mast cell neoplasia but not previously reported in horses.
Purpose of the Study:
- To report a case of equine mast cell neoplasia with metastasis.
- To document the association of eosinophilia with equine mast cell neoplasia.
- To highlight the rarity of metastasis in equine mast cell tumors.
Main Methods:
- Clinical examination and diagnostic imaging of a stallion with carpal lameness.
- Cytology and histopathology of subcutaneous biopsy and affected tissues.
- Fungal culture and serial full blood counts.
Main Results:
- Histopathology revealed a moderately well-differentiated mast cell neoplasm with metastasis to the axillary lymph node.
- Persistent mature eosinophilia and hyperfibrinogenaemia were noted.
- Gross examination showed connective tissue deposition, calcification, and necrotic debris around the carpus.
Conclusions:
- This case represents a rare instance of malignant mast cell neoplasia with metastasis in a horse.
- The concurrent eosinophilia is a novel finding in equine mast cell neoplasia.
- The study underscores the importance of thorough histopathological evaluation for rare equine cancers.
Abstract:
A 12-year-old Arab stallion was presented with a chronically swollen right carpus resulting in profound lameness of the same leg. An incisional biopsy of subcutaneous tissue from the right carpus submitted for cytology and histopathology revealed large numbers of eosinophils interspersed by substantial numbers of variably sized and granulated mast cells. Fungal culture of a subcutaneous tissue sample taken from the right carpus was negative. Serial full blood counts revealed persistent mature eosinophilia, not accompanied by a mastocytaemia, neutrophilia without left shift and persistent hyperfibrinogenaemia. After humane destruction, dissection of the affected limb revealed a thick layer of connective tissue deposited around the right carpal joint. Within the connective tissue were embedded many small 0.25-1 cm diameter yellow gritty nodules, which consisted of dystrophic calcification and necrotic cell debris. The tendons enveloped by the connective tissue mass had limited function. The right axillary lymph node was moderately enlarged, yellow-brown and moist. Histopathological examination revealed a moderately well differentiated mast cell neoplasm with evidence of metastasis to the regional lymph node. In horses, malignant mast cell neoplasia is rare, while metastasis has only been reported in one other horse. Eosinophilia associated with equine mast cell neoplasia has not been reported previously but is recorded in mast cell neoplasia in the dog.
