Morphological and immunohistochemical characteristics of diffuse seminoma in horses: A case report

The present study describes the morphological and immunohistochemical characteristics of a case of diffuse seminoma in a 16‐year‐old male mixed‐breed horse. According to the owner, the animal's left testicle had been gradually increasing in size over a period of 2 months. On palpation, the testicle had a firm consistency, with no sensitivity to digital pressure, was adhered to the scrotum and measuring 16 cm × 8 cm. In the ultrasound examination, it presented a heterogeneous texture and areas of hypoechogenic echogenicity without visualization of the mediastinum. Therefore, the bilateral orchiectomy was performed. After the surgical procedure, it was found that the affected testicle presented a firm mass measuring 9 cm × 7 cm × 3.5 cm. Histologically, a multilobulated, non‐encapsulated and invasive tumour mass was found, which replaced the seminiferous tubules, consisting of polygonal cells arranged in a mantle that varied from cohesive to loosely cohesive, supported by a scarce fibrous stroma. In the immunohistochemical examination, the neoplastic cells showed positive immunolabelling for OCT4 and C‐KIT. In this report, the physical examination combined with the ultrasonographic examination were fundamental to the therapeutic management of the case, and the final diagnosis was made after histopathological and immunohistochemical tests.