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Histiocytic sarcoma in the tarsus of a cat
Insights
A rare histiocytic sarcoma, a type of cancer, was diagnosed in a 12-year-old cat
Area of Science:
- Veterinary Pathology
- Oncology
- Immunohistochemistry
Background:
- A 12-year-old Persian cat presented with a tarsal swelling and enlarged popliteal lymph node.
- Initial cytologic evaluation suggested large cell lymphoma.
Purpose of the Study:
- To diagnose and characterize a neoplastic condition in a feline patient.
- To differentiate between potential diagnoses including lymphoma, synovial sarcoma, and histiocytic sarcoma.
Main Methods:
- Cytologic evaluation of fine-needle aspirates.
- Gross necropsy examination.
- Histopathological analysis of the mass and lymph node.
- Immunohistochemical staining for specific cell markers (cytokeratin, CD79a, CD3, CD18, vimentin, lysozyme, alpha-1-antitrypsin).
Main Results:
- Necropsy revealed a multi-lobulated subcutaneous mass involving the tarsus with muscular extension.
- Histology showed round cells with pleomorphic nuclei and eosinophilic cytoplasm, infiltrating the joint and lymph node.
- Immunohistochemistry results (negative for cytokeratin, CD79a, CD3; positive for CD18, vimentin, lysozyme, alpha-1-antitrypsin) were most consistent with histiocytic sarcoma.
Conclusions:
- The feline tumor was definitively diagnosed as histiocytic sarcoma based on combined histopathology and immunohistochemistry.
- This case represents the first reported instance of feline histiocytic sarcoma involving a joint.
Abstract:
A 12-year-old Persian cat was examined for a firm swelling of the right tarsal region and enlargement of the corresponding right popliteal lymph node. Cytologic evaluation demonstrated a population of malignant cells consistent with large cell lymphoma. Necropsy revealed a multi-lobulated subcutaneous mass involving the tarsus with some extension into adjacent deep muscular tissue. Histologically, the mass was composed of round cells with eosinophilic cytoplasm and pleomorphic anisokaryotic nuclei. Evidence of articular and nodal infiltration by these cells was observed. Differential diagnoses included synovial sarcoma and histiocytic sarcoma. Neoplastic cells were negative for cytokeratin, CD79a, and CD3 and positive for CD18, vimentin, lysozyme, and alpha-1-antitrypsin, most consistent with a diagnosis of histiocytic sarcoma. This is the first report of a histiocytic sarcoma involving a joint of a cat. The final diagnosis was based on the light microscopic appearance in combination with the immunohistochemical stains.
