Equis ISSN 2398-2977

Ovary: neoplasia - granulosa/theca cell

Contributor(s): Jean Pierre Held, Clare Knottenbelt, Prof Derek Knottenbelt, Rob Lofstedt, Philippa O'Brien


  • Granulosa theca cell tumors (GTCT) are the most common ovarian tumor in mares (2.5-4% of all equine neoplasia).
  • Originate from sex cord stromal tissue and are usually benign.
  • Cause:proliferation of granulosa cells due to dysregulation of several pathways associated with FSH receptors.
  • Signs: behavioral changes due to hormonal secretion, including nymphomania and stallion-like behavior; irregular estrous cycles or failure to cycle; large tumors may cause colic signs.
  • Diagnosis: rectal palpation, ultrasonography, serum hormone levels, histopathology.
  • Treatment: surgical excision of affected ovary.
  • Prognosis: good after surgery.



  • Unregulated granulosa cell proliferation following FSH receptor binding, due to dysregulation of signaling pathways.
  • No mutations on the FSH receptor have been detected.

Predisposing factors

  • None.
  • GTCT can occur in any filly or mare, irrespective of breeding history; has even been reported in neonates.
  • GTCT can also occur in pregnant mares.


  • Granulosa theca cell tumors originate from sex cord and stromal ovarian tissue. Most are composed of both granulosa and theca cells, although the relative proportions vary.
  • GTCTs are usually benign.
  • More commonly unilateral, occasionally bilateral.
  • Many GTCTs are hormonally active; clinical signs vary depending on hormonal secretion.
  • Around 80-85% of mares with GTCT have elevated inhibin levels.
  • Inhibin suppresses FSH secretion by direct effect on anterior pituitary, causing the dominant follicle to grow and produce estrogen.
  • Inhibin secretion is also thought to suppress activity in the non-affected ovary.
  • Testosterone levels are elevated in around 50% of mares with GTCT.
  • GTCTs with a larger theca cell component are thought to be more likely to produce testosterone.
  • Anti-Mullerian hormone (ANH) levels are increased in 95% of mares with GTCT.
  • Progesterone levels are usually low (<1 ng/mL) but may be elevated early in the course of disease, if the mare is still cycling, or in pregnant mares.


  • Chronic.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Hector R C & Cruz A M (2014) Ascites in a 13-year-old miniature horse mare with an ovarian granulosa theca-cell tumour: A manifestation of Meigs' syndrome. Equine Vet Educ 26 (5), 237-241 VetMedResource. 
  • Cameron I J (2014) Granulosa cell tumours - diagnostic considerations. Equine Vet Educ 26 (5), 242-243 WileyBlackwell.
  • Ball B A, Almeida J & Conley A J (2013) Determination of serum anti-Mullerian hormone concentrations for the diagnosis of granulosa-cell tumours in mares. Equine Vet J 45 (2), 199-203 PubMed.
  • Crabtree J R et al (2013) Granulosa cell tumour: An interesting case in a pregnant mare. Equine Vet Educ 25 (1), 4-10 VetMedResource.
  • McCue P M (2013) Tumour, or not tumour, that is the question. Equine Vet Educ 25 (1), 11-14 VetMedResource.
  • Packer M & McKane S (2012) Granulosa thecal cell tumour in a mare causing hypertrophic osteopathy. Equine Vet Educ 24 (7), 351-356 VetMedResource.
  • Almeida J et al (2011) Biological and clinical significance of anti-Mullerian hormone determination in blood serum of the mare. Theriogenology 76 (8), 1393-1403 PubMed.
  • Crabtree J (2011) Review of seven cases of granulosa cell tumour of the equine ovary. Vet Rec 169 (10), 251 PubMed.
  • Harper J et al (2010) Ultrasonographic appearance and abdominal haemorrhage associated with a juvenile granulosa cell tumour in a foal. Equine Vet Educ 22 (3), 115-120 VetMedResource.
  • McKinnon A O & Barker K J (2010) Granulosa theca cell tumours. Equine Vet Educ 22 (3), 121-124 WileyBlackwell.
  • Henson F M D & Dobson J M (2004) Use of radiation therapy in the treatment of equine neoplasia. Equine Vet Educ 16 (6), 315-318 VetMedResource.
  • Rambags B P B, Stout T A E & Rijkenhuizen (2003) Ovarian granulosa cell tumours adherent to other abdominal organs; surgical removal from 2 Warmblood mares. Equine Vet J 35 (6), 627-632 PubMed.
  • Mair T S (2002) Small colon impaction associated with a granulosa cell tumor in a pony mare. Equine Vet Educ 14 (1), 17-18 VetMedResource.
  • Watson E D (1999) Granulosa cell tumors in the mare - a review of 9 cases. Equine Vet Educ 11 (3), 136-142 VetMedResource.
  • Ragle C A, Southwood L L, Hopper S A & Boute P L (1996) Laparoscopic ovariectomy in 2 horses with granulosa cell tumors. JAVMA 209 (6), 1121 PubMed.
  • Gift L J, Gaughan E M & Schoning P (1992) Metastatic granulosa cell tumor in a mare. JAVMA 200 (10), 1525-1526 PubMed.
  • Hinrichs K & Hunt P R (1990) Ultrasound as an aid to diagnosis of granulosa cell tumor in the mare. Equine Vet J 22 (2), 99-103 PubMed.
  • White R A S & Allen W R (1985) Use of ultrasound echography for the differential diagnosis of a granulosa cell tumor in a mare. Equine Vet J 17 (5), 401-402 PubMed.
  • Stickle R L, Erb R E, Fessler J F & Runnels L J (1975) Equine granulosa cell tumors. JAVMA 167 (2), 148-151 PubMed.

Other sources of information

  • Card C E (2011) Ovarian Neoplasia. In: Equine Reproduction. Eds: McKinnon A O, Squires E L, Vaala W E & Varner D D. Wiley-Blackwell. pp 2707-2716.