Original Research A Retrospective Analysis of 2,253 Cases Submitted for Endocrine Diagnosis of Possible Granulosa Cell Tumors in Mares Barry A. Ball DVM, PhD, DACT a, * , Alan J. Conley BVSc, PhD d , Juliana Almeida DVM, PhD b , Alejandro Esteller-Vico DVM, PhD a , James Crabtree BVM&S, MRCVS c , Coralie Munro BS d , Irwin K.M. Liu DVM, PhD d a Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington, KY b Universidade de Fortaleza, Ceará, Brazil c Equine Reproductive Services Ltd, Messenger Farm, Ryton, Malton, United Kingdom d Department of Population Health and Reproduction, School of Veterinary Medicine, University of California Davis, Davis, CA article info Article history: Received 18 April 2013 Received in revised form 28 May 2013 Accepted 9 July 2013 Available online xxxx Keywords: Equine Granulosa cell tumor Inhibin Testosterone Progesterone Anti-Müllerian hormone abstract Endocrine diagnoses of granulosa cell tumors (GCTs) in the mare are frequently based upon determination of serum concentrations of inhibin, testosterone, and progesterone (GCT panel). In the present study, we examined results from 2,253 samples submitted for determination of GCT panel. In an additional subset of samples (n ¼ 75), diagnosis of GCT was confirmed based upon surgery or necropsy. The objective of the current study was to examine the agreement between serum inhibin and testosterone concentrations in mares with serum progesterone concentrations less than or 1 ng/mL. Across all samples, elevations in serum inhibin or testosterone were noted in 15.2% or 17.3% of samples, respectively. For samples with progesterone <1 ng/mL, more (P ¼ .001) samples had elevated inhibin than elevated testosterone, whereas for samples with progesterone 1 ng/mL, more (P < .0001) samples had elevated testosterone than elevated inhibin. For samples with progesterone <1 ng/mL, the agreement between elevated inhibin and testosterone was greater than that for samples with progesterone 1 ng/mL. In a subset of 53 samples with progesterone 1 ng/mL, 28 samples had endocrine evidence of a gran- ulosa cell tumors based upon elevations of serum anti-Müllerian hormone, and 4 of these samples had endocrine evidence of pregnancy based upon estrone sulfate concentrations. For samples from mares with confirmed GCTs, 85% and 55% had elevated inhibin or testosterone, respectively. Based upon endocrine diagnosis, GCTs occur in mares with elevated progesterone and/or estrone sulfate, albeit at a low rate. Ó 2013 Elsevier Inc. All rights reserved. 1. Introduction Granulosa cell tumors (GCTs) are the most common ovarian tumor in mares [1]. These tumors are detected at a mean age of 10.6 years [2], although GCTs have been re- ported in prepubertal fillies and neonates [3-5]. When most GCTs are diagnosed, they are often associated with the cessation of normal estrous cycles [6] because of the suppression of the remaining normal ovary [7]. Clinically, endocrine diagnosis of GCTs in the mare is based most often upon determination of serum concentrations of inhibin, testosterone, and progesterone (GCT panel [7]). Increased serum concentrations of inhibin or testosterone or both along with low circulating progesterone concen- trations in nonpregnant mares have been used for endo- crine confirmation of GCTs in mares [6,8-10]. Testosterone and inhibin were elevated in 50% and 87%, respectively, of * Corresponding author at: Dr. Barry A. Ball, DVM, PhD, DACT, Univer- sity of Kentucky, Gluck Equine Research Center, Dept. of Veterinary Science, Lexington, KY 40546. E-mail address: b.a.ball@uky.edu (B.A. Ball). Contents lists available at SciVerse ScienceDirect Journal of Equine Veterinary Science journal homepage: www.j-evs.com 0737-0806/$ – see front matter Ó 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jevs.2013.07.005 Journal of Equine Veterinary Science xx (2013) 1–7