Fulminant multicentric osteosarcoma with systemic metastasis in a dog

A 15-year-old castrated mixed breed dog presented due to a 5-month history of cough and difficulty in ambulation. Necropsy showed multiple periosteal and intramedullary infiltrative masses in the appendicular skeleton. In addition, single and multiple neoplastic nodules were observed in several organs, including the lungs, liver, kidney, and heart. Microscopically, several skeletal neoplastic masses and nodules in the parenchymal organs revealed similar changes. The neoplastic cells were spindle- to polygonal-shaped with prominent osteoid production and occasional cartilaginous and bone formation. Based on the gross findings and histopathology results, the case was diagnosed as multicentric osteosarcoma with systemic metastases.