Diagnostic Marker, Horse; Ovary; Tumor eng Immunohistochemical markers for equine granulosa cell tumors: a pilot study Dolin, Aurelia (Veterinary Practice Tierdoc) Schweiger, Peter (Veterinary Practice Tierdoc) Waselau, Martin (Equine Hospital Aschheim) Egerbacher, Monika (UMIT - Private Universität für Gesundheitswissenschaften, Medizinische Informatik und Technik) Walter, Ingrid (University of Veterinary Medicine Vienna) Sex cord-stromal tumors (SCSTs), generally referred to as granulosa cell tumors (GCTs) or granulosa-theca cell tumors (GTCTs) in equids, show complex compositions and variable numbers of hormone-producing cells. These tumors can be difficult to diagnose, especially in early stages. Therefore, we tested a panel of antibodies for vimentin, smooth muscle actin, laminin, Ki-67, E-cadherin, calretinin, moesin, p-ezrin, AMH, and aromatase, markers used for tumor composition and classification, progression, and prognosis in human SCSTs, on an exemplary grapefruit-size equine GCT within the left ovary of a 13-year-old mare with stallion-like behavior and elevated testosterone levels in comparison with normal ovarian tissue. The tumor showed a low proliferation rate and prominent moesin and p-ezrin staining in granulosa cells. E-cadherin, calretinin, aromatase, and AMH are suggested to be potential markers for different cell components of equine SCSTs that can support tumor diagnosis and classification. application/pdf Journal of Equine Science 34(2), 37-46 (2023) article CC BY-NC-ND 4.0 International http://creativecommons.org/licenses/by-nc-nd/4.0/ J-Stage 2023 doi:10.1294/jes.34.37 https://phaidra.vetmeduni.ac.at/o:3589