34th Annual Scientific Meeting proceedings

Objectives:

Equine testicular seminomas are infrequently reported in the literature and long-term survival is unknown. To report the clinical features and outcome of cases of histopathologically confirmed seminoma.

Methods:

Medical records of nine horses diagnosed with testicular seminoma between 2000 and 2024 were reviewed. Horses were included if seminoma was confirmed on histopathology from biopsy or necropsy. Information retrieved included signalment, history, clinical pathology, ultrasound findings, treatment and outcome.

Results:

Median age was 18 years (range 8-26). Three of 9 horses presented for systemic disease; colic (2) and ventral edema (1). All three were euthanized after identification of abdominal masses on ultrasound. Six horses presented for testicular enlargement (5) or cryptorchid castration (1) and had the abnormal testicles submitted for histopathology. All testicles had lymphatic and/or vessel invasion, but a clean surgical margin. Five horses were euthanized between 4 months and 3 years post castration due to acute weight loss with subsequent abdominal masses identified on palpation or ultrasound. One horse was euthanized 3 years post discharge for lameness with no signs attributable to the previously diagnosed seminoma. Necropsy was available in 5 horses which identified large caudal abdominal masses consistent with metastatic spread of seminoma to the lumbar lymph nodes. Metastases were also identified in the liver, spleen and pericardium.

Conclusions:

Testicular seminoma had a high rate of metastasis in this case series and a poor long-term prognosis. Horses that present for testicular enlargement should undergo diagnostic screening, including abdominal ultrasound, to determine the possible presence of metastasis in cases of testicular seminoma.