Osteosarcoma in an American robin (Turdus migratorius).

An osteosarcoma arising from the left hemimandible was diagnosed in an adult American robin (Turdus migratorius). Neoplastic spindle cells were observed extending away from foci of trabecular bone in dense sheets, occasionally within osteoid tissue. The variably pleomorphic spindle cells contained fibrillar, lightly basophilic cytoplasm, irregular, round to ovoid nuclei, and single or multiple small nucleoli. This is the first report of an osseous neoplasm in a wild passerine.