P‐62 Dermal and subcutaneous extraskeletal osteosarcomas in eight dogs, two cats, and one ferret

Abstract

Osteosarcoma is a malignant mesenchymal neoplasm characterized by the formation of osteoid tissue. It is the most frequent primary bone tumour in dogs, accounting for nearly 80–85% of all reported long bone appendicular osteosarcomas. Conversely, in cats and other species, osteosarcoma is rare at any site. Extraskeletal osteosarcoma (EOS) is a malignant, osteoid‐producing neoplasm without primary periosteal or bone involvement. These tumours have been described less frequently and occur mainly in the mammary glands of female dogs. Case material was obtained from biopsy records of the Pathology Service at the Veterinary School, Universidad Nacional. The diagnosis of these tumours was based on the absence of clinical, radiological, or pathological evidence of primary bone or glandular involvement. Samples were processed for histopathological examination and stained with H&E. In two cases, immunohistochemistry was performed. Eleven cases were diagnosed with EOS located in two histological locations. The dermal group consisted of three female dogs (two Rottweillers and one Fila Brasileiro), one male German shepherd (mean age of dogs: 5.5 years), two female cats (mixed‐breed and Siamese) of 5 and 11 years of age, respectively, and one 4‐year‐old female ferret. The subcutaneous group consisted of four dogs, two female pit bull terriers and two male dogs (boxer and mixed‐breed), with a mean age of 5 years. The subcutaneous EOS tumours were more aggressive. Three dogs were euthanized due to lung metastasis and the remaining dog was lost to follow‐up. Funding: Self‐funded.