Equis ISSN 2398-2977

Testis: neoplasia - overview

Synonym(s): Testicular tumor, testicular cancer

Contributor(s): Prof Derek Knottenbelt, Joyce Parlevliet, Anna Hollis

Introduction

  • Tumors of the testicle are uncommon; the incidence is unknown as most male horses are castrated at an early age; tumors are usually unilateral.  
  • The relatively high number of geldings in most equine populations means that testicular tumors are probably best regarded as unusual in entire males, rather than rare.
  • There is a well-established relationship between cryptorchidism and testicular neoplasia. The increased temperature of the abdomen compared to the normal testicular location increases the risk of neoplasia. Cryptorchid horses should therefore be castrated as routine.
  • Testicular tumors are divided for descriptive purposes into:
    • Germ cell tumors.
    • Non-germinal tumors.

Germ cell tumors

  • Seminoma Testis: neoplasia - seminoma:
    • The most common tumor of the equine testicle.
    • Aged stallions are most often affected.
    • May affect cryptorchid or descended testicles.
    • No endocrinological function or implications.
    • Usually unilateral but occasional bilateral cases are seen.
    • Leads to slow, non-painful enlargement of one or both testicles.
  • Teratoma Teratoma and teratocarcinoma:
    • Teratomas are relatively common, affecting younger horses.
    • They arise directly from the cells of the seminiferous epithelium and therefore can transform into endoderm, mesoderm or ectoderm.  
    • For this reason, on cut surface, these tumors will have many different types of tissue, including differentiated hair, fat, teeth and bone.  
    • Usually benign lesions.
    • The tumors are usually round or oval with irregular surfaces.  
    • Teratomas are usually cystic.
    • They are most common in retained abdominal testicles.
    • Most commonly found incidentally during castration.
    • May be unilateral or bilateral.
    • Teratocarcinomas are extremely rare, malignant tumors with high metastatic potential.
    • Any suspicion of teratocarcinoma should lead to histopathology being performed to ensure the correct diagnosis is achieved.

Non-germinal tumors

  • Interstitial (Leydig) cell tumors:
    • These are rare in the horse. 
    • They are usually small and may be multiple in number and are usually found incidentally at necropsy or after castration. 
    • Benign, slow-growing lesions.
    • Can be functional, producing androgens and leading to behavioral changes (such as aggression).
    • Good prognosis and unilateral castration. 
  • Sertoli (sustentacular) cell tumors:
    • These are rare in the horse.
    • More commonly found in cryptorchid testicles Testis: cryptorchidism but also reported in descended testicles.
    • Leads to infertility.
    • Only been reported in mature and aged stallions.

Predisposing factors

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Clinical signs

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Diagnosis/differential diagnosis

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Treatment

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Prognosis

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Valentine B A (2009) Equine testicular tumours. Equine Vet Educ 21 (4), 177-178.
  • 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.
  • Misdorp W (2003) Congenital tumours and tumour-like lesions in domestic animals - 3 Horses - A review. Vet Q 25 (2), 61-71 PubMed.
  • Pratt S M, Stacy B A et al (2003) Malignant sertoli cell tumor in the retained abdominal testis of a unilaterally cryptorchid horse. JAVMA 222 (4), 486-490 PubMed.
  • Hoagland T A et al (1986) Effects of unilateral castration on morphological characteristics of the testis in one-, two-, and three-year old stallions. Theriogenology 26, 397-405.
  • Trigo F J, Miller R A & Torbeck R L (1984) Metastatic equine seminoma:  Report of two cases. Vet Pathol 21, 259-300 PubMed.
  • Rahaley R S, Gordon B J, Leiopold H W & Peter J E (1983) Sertoli cell tumor in a horse. Equine Vet J 15, 68-69 PubMed.
  • Nachtsheim D A, Scheible F W, Nachtsheim D & Gosink B B (1979) High resolution ultrasonography of scrotal pathology. Radiology 131, 719-722 PubMed.
  • Vaillancout D, Fretz P & Orr J P (1979) Seminoma in the horse: Report of two cases. J Eq Med Surg 3, 213-218.
  • Smith H A (1954) Interstitial cell tumor of the equine testis. JAVMA 124, 356-357 PubMed.

Other sources of information

  • Mckinnon A O & Voss J L (1993) Equine Reproduction. Lea & Febiger, USA. pp 871-877.


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