In equine medicine, what is the most common tumor of the penis?

• A. Lymphoma
• B. Fibrosarcoma
• C. Squamous cell carcinoma
• D. Melanoma

Answer: (C)

Penile squamous cell carcinoma is the most common tumor on the horse’s penis. It arises from the surface squamous epithelium of the glans and prepuce and is linked to sun exposure and chronic irritation, which together encourage malignant transformation of the epithelial cells. Clinically, you’ll see a proliferative or ulcerative mass on the penis that can invade deeper tissues; confirming with a biopsy shows invasive squamous epithelium. Treatments are most successful when the tumor is localized and may include surgical removal or penile resection, with prognosis depending on how far the disease has spread. Other tumors can occur in horses, but they are not as typical for the penis: lymphomas are a broader systemic disease, fibrosarcomas are less common on the penis, and melanoma, while possible—especially in gray horses—does not occur as commonly there as squamous cell carcinoma.