Primary Sublingual S100-Positive Undifferentiated Pleomorphic Sarcoma in a Cat: A Case Report with Comprehensive Exclusionary Immunohistochemistry.

Authors

Yoo Suk Kim, Hwi-Yool Kim, Kwangsik Jang

Published in

Veterinary sciences. Volume 13. Issue 10. Sep 30, 2026. Epub Sep 30, 2026.

Abstract

Undifferentiated pleomorphic sarcoma (UPS) is an exceptionally rare mesenchymal neoplasm in the feline oral cavity, presenting significant diagnostic and therapeutic challenges. A 10-year and 10-month-old, castrated male Korean Shorthair cat presented with a progressively enlarging sublingual mass measuring 2.77 cm × 3.02 cm × 1.86 cm. Computed tomography revealed a well-circumscribed, non-osteolytic sublingual mass without detectable mandibular bone erosion or regional lymphadenopathy. Gross complete surgical excision was performed via a transoral approach without mandibulectomy. Histopathological examination revealed a highly pleomorphic, sheet-like proliferation of atypical spindle to epithelioid cells with prominent giant binucleated cells and a low mitotic count (3 per 10 high-power fields). To establish a diagnosis of exclusion, an extensive immunohistochemical (IHC) panel was performed. The neoplastic cells were strongly positive for vimentin and diffusely positive for S100, but immunonegative for pancytokeratin (PanCK), Melan-A, Iba-1, desmin, and α-smooth muscle actin (α-SMA). These exclusionary IHC findings did not support epithelial, histiocytic, or myogenic differentiation, though amelanotic melanoma cannot be completely excluded based on Melan-A negativity alone. Rather than confirming definitive neural differentiation, the diffuse S100 immunoreactivity supported a final diagnosis of an S100-positive UPS. The patient achieved rapid functional recovery, with owner-reported absence of clinical signs of local recurrence over a 90-day follow-up period. This report underscores the necessity of a broad exclusionary IHC panel to accurately diagnose feline oral UPS and highlights surgical resection as a viable local management option.

PMID:
42944132
Bibliographic data and abstract were imported from PubMed on 27 Oct 2026.

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