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Testicular seminoma: clinical, imaging, and histologic features in nine horses.
Abstract: Testicular seminomas in horses are infrequently reported in the veterinary literature and long-term survival and metastatic potential are not well documented. Objective: Describe the clinical, imaging, and histologic features in 9 horses with testicular seminoma. Methods: Medical records of 9 horses diagnosed with testicular seminoma at a referral hospital between 2000 and 2024 were reviewed. Methods: Horses were included if seminoma was confirmed on histopathology from biopsy or necropsy. Information retrieved included signalment, history, clinical pathology, ultrasonographic findings, treatment, and outcome. Results: Median age was 18 years (range, 8-26). Three of 9 horses presented for systemic disease (colic, 2; ventral edema, 1). All 3 had large abdominal masses palpable on rectal examination and were euthanized after diagnostic evaluation. Six horses presented for unilateral testicular enlargement (5) or cryptorchid castration (1). These horses underwent castration and the removed testes had features of malignancy with lymphatic neoplastic emboli. Five of 6 horses were euthanized between 4 months and 3 years after castration because of acute weight loss and abdominal masses identified on rectal examination or ultrasonographic examination, attributable to metastatic spread. One additional horse was euthanized for unrelated reasons. Conclusions: Horses presented with testicular enlargement and diagnosis of testicular seminoma should undergo diagnostic screening, including transabdominal or transrectal ultrasonographic examination to determine the presence of possible metastasis. Negative screening results at the time of diagnosis do not rule out the possibility of metastasis, and frequent screening at regular intervals is prudent in such cases. Horses with testicular seminoma of retained or descended testicles have a poor long term prognosis because of high potential for metastatic spread.
© The Author(s) 2026. Published by Oxford University Press on behalf of the American College of Veterinary Internal Medicine.
Publication Date: 2026-07-07 PubMed ID: 42407252PubMed Central: PMC13336631DOI: 10.1093/jvimsj/aalag129Google Scholar: Lookup The Equine Research Bank provides access to a large database of publicly available scientific literature. Inclusion in the Research Bank does not imply endorsement of study methods or findings by Mad Barn.
- Journal Article
Summary
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Overview
- This study reports on the clinical signs, imaging findings, histology, treatment, and outcomes of nine horses diagnosed with testicular seminoma, a type of testicular cancer.
- It highlights the aggressive metastatic potential of this tumor in horses and stresses the importance of thorough and regular screening for metastasis even after initial treatment.
Background and Objective
- Testicular seminoma is a rare tumor in horses, with limited cases discussed in veterinary literature.
- There is insufficient information on long-term survival and the likelihood of the cancer spreading (metastasis) in horses.
- The research aimed to describe clinical symptoms, imaging characteristics, histologic features, treatment approaches, and outcomes in nine horses with this disease.
Methods
- The data were collected retrospectively from medical records of horses seen at a referral hospital over a 24-year span (2000–2024).
- Horses were included only if the testicular seminoma diagnosis was confirmed by histopathological examination of biopsy or necropsy specimens.
- Information extracted included:
- Basic information (age, signalment)
- Clinical history and presenting signs
- Laboratory test results (clinical pathology)
- Ultrasound findings of testicular and abdominal structures
- Treatment performed
- Outcome, including survival and reason for euthanasia if applicable
Results
- Median age was 18 years, with a range from 8 to 26 years old, indicating this tends to affect older horses.
- Three horses initially showed signs of systemic illness including colic and ventral (under-belly) edema.
- All three had palpable large abdominal masses detected via rectal examination and were euthanized after diagnostic workup.
- Six horses presented either with unilateral testicular enlargement (5 horses) or for castration due to retained (cryptorchid) testicles (1 horse).
- All six underwent castration removing the affected testis, which histologically showed malignancy and neoplastic emboli in lymph vessels.
- Despite castration, 5 of these 6 horses developed metastatic disease evidenced by abdominal masses and weight loss between 4 months and 3 years, leading to euthanasia.
- One horse was euthanized for reasons unrelated to the seminoma.
Conclusions and Clinical Implications
- Horses with testicular enlargement should be evaluated carefully with imaging, including transabdominal or transrectal ultrasound, to look for metastases beyond the testis.
- Even if initial screening does not find metastasis, it does not guarantee the cancer will not spread later; therefore, regular and ongoing screening is recommended.
- The prognosis for horses with testicular seminoma, whether the testis is descended or retained, is poor due to the high likelihood of metastasis.
- This study underscores the need for veterinarians to monitor these horses closely after diagnosis and treatment for early detection of metastatic disease.
Cite This Article
APA
Ratliff B, Kilcoyne I, Dini P, Katzman SA, Miklavcic M, Chromik M, Choi E, Vaughan B.
(2026).
Testicular seminoma: clinical, imaging, and histologic features in nine horses.
J Vet Intern Med, 40(4), aalag129.
https://doi.org/10.1093/jvimsj/aalag129 Publication
Researcher Affiliations
- Comstock Equine Hospital, Reno, NV, United States.
- Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California-Davis, Davis, CA, United States.
- Department of Population Health and Reproduction, School of Veterinary Medicine, University of California-Davis, Davis, CA, United States.
- Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California-Davis, Davis, CA, United States.
- Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California-Davis, Davis, CA, United States.
- Department of Pathology, Microbiology, and Immunology, School of Veterinary Medicine, University of California-Davis, Davis, CA, United States.
- Department of Pathology, Microbiology, and Immunology, School of Veterinary Medicine, University of California-Davis, Davis, CA, United States.
- Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California-Davis, Davis, CA, United States.
MeSH Terms
- Animals
- Male
- Horses
- Testicular Neoplasms / veterinary
- Testicular Neoplasms / pathology
- Testicular Neoplasms / diagnostic imaging
- Horse Diseases / pathology
- Horse Diseases / diagnostic imaging
- Seminoma / veterinary
- Seminoma / pathology
- Seminoma / diagnostic imaging
- Seminoma / surgery
- Orchiectomy / veterinary
- Ultrasonography / veterinary
- Retrospective Studies
Conflict of Interest Statement
The authors declare no conflicts of interest.
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