# Ovarian Sex Cord Stromal Tumor in a Free-Ranging Brown Bear (Ursus arctos)

## TL;DR

This paper reports the first case of a malignant ovarian tumor in a wild brown bear, diagnosed using histopathology and immunohistochemistry.

## Contribution

The study presents the first documented case of an ovarian sex cord stromal tumor in the bear family (Ursidae).

## Key findings

- The tumor was identified as a steroid cell tumor based on histopathological and immunohistochemical analysis.
- The tumor showed INHA-positive immunostaining and inflammatory cell infiltration, including macrophages and B lymphocytes.
- This case represents the first report of an ovarian sex cord stromal tumor in the bear family.

## Abstract

Here, we describe an unusual metastatic ovarian sex cord stromal tumor in a 14-year-old free-ranging female Eurasian brown bear (Ursus arctos) from Northwestern Spain. Based on histopathological and immunohistochemical studies, the tumor was diagnosed as a steroid cell tumor, not otherwise specified.

Reports on neoplasms in bears are scarce, especially concerning ovarian tumors. A large primary ovarian neoplasm with multiple metastasis was found during the necropsy of a 14-year-old free-ranging Eurasian brown bear (Ursus arctos) from Northwestern Spain. Histopathology and immunohistochemistry allowed for the diagnosis of a sex cord stromal tumor. This is a complex group of neoplasms which differ in the predominant cell morphology and immunohistochemical features. The microscopic examination revealed two types of cells, one with eosinophilic cytoplasm, intermingled with larger vacuolated cells rich in lipids. The evaluation of the immunoreactivity to different markers, frequently used in the characterization of gonadal tumors (INHA, inhibin-alpha; PLAP, placental alkaline phosphatase; Ki-67; α-SMA, actin alpha-smooth muscle) and inflammation patterns (IBA1, ionized calcium-binding adapter molecule for macrophages; CD3 for T lymphocytes; CD20 for B lymphocytes), displayed significant INHA positive immunostaining of neoplastic cells, as well as inflammatory cell infiltration, mainly composed of macrophages and B lymphocytes. These findings were consistent with a malignant ovarian steroid cell tumor, not otherwise specified. The present study characterizes an unusual type of neoplasm, and also represents the first report of an ovarian sex cord stromal tumor in Ursidae.