Primary Ovarian Leiomyoma in a White Tiger (Panthera tigris)

SIMPLE SUMMARY: Reproductive system cancers occur frequently in captive non-domestic felids, negatively impacting wildlife conservation by affecting reproduction. Ovarian tumours are very rare and occasionally mentioned in retrospective studies of large numbers of wild felids aimed at determining tumour types, prevalence rates, and species distribution. In this report, we describe the occurrence of an ovarian leiomyoma in a 22-year-old white tiger (Panthera tiger) treated with a gonadotropin-releasing hormone (GnRH) agonist to control reproduction, detailing histomorphological and immunohistochemical characteristics. Reproductive cancer affects reproduction, and since maintenance of fertility in large felids is essential for captive breeding programs, it is important to regularly monitor animals for development of neoplasia, allowing for early diagnosis and effective management. Finally, the possible role of contraceptives in the pathogenesis of cancer in non-domestic felids is worthy of future investigation. ABSTRACT: Ovarian leiomyomas are very rare in domestic cats and occasionally mentioned in studies reporting general pathological findings and neoplasm occurrence in non-domestic large felids. This report describes a case of ovarian leiomyoma in a 22-year-old white tiger (Panthera tiger), treated with deslorelin implants, detailing pathological and immunohistochemical characteristics. Gross examination revealed a markedly enlarged, firm, whitish right ovary with a multinodular appearance. On a cut surface, multiple brown-fluid-filled cysts interspersed with solid grey-to-white areas were observed. On histopathological examination, the ovary was enlarged and replaced by a densely cellular neoplasm composed of spindle cells arranged in fascicles, or occasionally in a herringbone pattern, embedded in a large stroma of collagenous connective tissue. Neoplastic cells showed mild nuclear atypia and pleomorphism and low mitotic rate. Immunohistochemistry confirmed smooth muscle origin of the neoplasm, and cells were positive for vimentin, alpha-smooth muscle actin, desmin, and caldesmon. A low rate (<1%) of Ki-67-positive cells was observed. Although rare, ovarian leiomyoma should be considered when a mass is present in the ovary of a tiger with reproductive failure. Because cancer of the reproductive system impacts on species conservation by affecting reproduction, regular health monitoring is warranted to support wildlife conservation. Finally, the adverse effects associated with long-term treatment with synthetic GnRH analogues as contraceptives in non-domestic felids are worthy of future investigation.