Osteosarcoma of the patella in a dog

Osteosarcoma of the patella was diagnosed by biopsy in a 9-year-old, male dog of mixed breeding. The dog was originally examined because of intermittent lameness of the left hindlimb; there were minimal palpable abnormalities of the stifle. After the diagnosis, the owner refused further treatment for the dog. The dog was reexamined 13 months later because of a marked swelling of the stifle. The dog was euthanatized and necropsy findings confirmed the diagnosis.