An ovarian sex cord-stromal tumor with fibromatous and thecomatous differentiation in an Ezo brown bear (Ursus arctos yesoensis).

Authors

Mirei Shimada, Kyogo Hagino, Kazuya Matsuda, Yuto Sano

Published in

The Journal of veterinary medical science. Oct 06, 2026. Epub Oct 06, 2026.

Abstract

A mass was found in the left ovary of a 40-year-old captive female Ezo brown bear (Ursus arctos yesoensis) during a necropsy. Histopathology revealed two morphologically distinct stromal cell populations: round to polygonal cells with cytoplasmic microvacuoles, which were positive for inhibin-α and adipose differentiation-related protein (ADRP) and were surrounded by reticulin fibers, and spindle-shaped cells expressing α-smooth muscle actin, which produced collagen and exhibited occasional ADRP-positivity. The ovary also contained cystic and cauliflower-like nodular lesions covered by ovarian surface epithelium. The mass was diagnosed as an ovarian sex cord-stromal tumor with fibromatous and thecomatous differentiation. The cystic lesions were interpreted as surface epithelial cysts, although a subsurface epithelial structures-like origin could not be excluded. The cauliflower-like nodular lesion was described as a stromal protrusion covered by ovarian surface epithelium. This case expands the spectrum of ovarian lesions reported in ursids and contributes to our understanding of reproductive pathology.

PMID:
42844162
Bibliographic data and abstract were imported from PubMed on 08 Oct 2026.

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