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 fromPubMed andVetMedResource.
  • 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 Educ26(5), 237-241VetMedResource. 
  • Cameron I J (2014)Granulosa cell tumours - diagnostic considerations.Equine Vet Educ26(5), 242-243WileyBlackwell.
  • 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 J45(2), 199-203PubMed.
  • Crabtree J R et al(2013)Granulosa cell tumour: An interesting case in a pregnant mare.Equine Vet Educ25(1), 4-10VetMedResource.
  • McCue P M (2013)Tumour, or not tumour, that is the question.Equine Vet Educ25(1), 11-14VetMedResource.
  • Packer M & McKane S (2012)Granulosa thecal cell tumour in a mare causing hypertrophic osteopathy.Equine Vet Educ24(7), 351-356VetMedResource.
  • Almeida Jet al(2011)Biological and clinical significance of anti-Mullerian hormone determination in blood serum of the mare.Theriogenology76(8), 1393-1403PubMed.
  • Crabtree J (2011)Review of seven cases of granulosa cell tumour of the equine ovary.Vet Rec169(10), 251PubMed.
  • Harper Jet al(2010)Ultrasonographic appearance and abdominal haemorrhage associated with a juvenile granulosa cell tumour in a foal.Equine Vet Educ22(3), 115-120VetMedResource.
  • McKinnon A O & Barker K J (2010)Granulosa theca cell tumours.Equine Vet Educ22(3), 121-124WileyBlackwell.
  • Henson F M D & Dobson J M (2004)Use of radiation therapy in the treatment of equine neoplasia.Equine Vet Educ16(6), 315-318VetMedResource.
  • 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 J35(6), 627-632PubMed.
  • Mair T S (2002)Small colon impaction associated with a granulosa cell tumor in a pony mare.Equine Vet Educ14(1), 17-18VetMedResource.
  • Watson E D (1999)Granulosa cell tumors in the mare - a review of 9 cases.Equine Vet Educ11(3), 136-142VetMedResource.
  • Ragle C A, Southwood L L, Hopper S A & Boute P L (1996)Laparoscopic ovariectomy in 2 horses with granulosa cell tumors.JAVMA209(6), 1121PubMed.
  • Gift L J, Gaughan E M & Schoning P (1992)Metastatic granulosa cell tumor in a mare.JAVMA200(10), 1525-1526PubMed.
  • Hinrichs K & Hunt P R (1990)Ultrasound as an aid to diagnosis of granulosa cell tumor in the mare.Equine Vet J22(2), 99-103PubMed.
  • 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 J17(5), 401-402PubMed.
  • Stickle R L, Erb R E, Fessler J F & Runnels L J (1975)Equine granulosa cell tumors.JAVMA167(2), 148-151PubMed.

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.