A nine-year-old, intact female, Chihuahua dog presented to their veterinarian for a solitary mass on the caudal most left mammary gland. The mass was excised and submitted to the Texas A&M Veterinary Medical Diagnostic Laboratory (TVMDL) for histopathology. Histologically, hyperplastic mammary tissue was infiltrated with a multilobular, unencapsulated, poorly demarcated neoplasm. Based on cellular morphology this tumor was diagnosed as a mammary gland sarcoma (fibrosarcoma).
Mammary tumors are common in older female dogs that are intact or were spayed after 2 years of age. Approximately half of all mammary tumors in dogs are benign and half are malignant. Mammary sarcomas are quite rare in dogs, accounting for approximately 10-15% of canine mammary neoplasia. Sarcomas are usually large, often seemingly well demarcated, and firm to bony. Fibrosarcomas and osteosarcomas are the most frequent mammary sarcomas in the dog. Mammary sarcomas are associated with an unfavorable prognosis due to a high tendency for local recurrence and metastases to regional lymph nodes and/or lungs.
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