Development of small-cell osteogenic sarcoma after ulnar ostectomy in a dog.

A 5-year-old male Saint Bernard was evaluated for vague forelimb lameness. Four and a half years earlier, the dog had undergone left ulnar ostectomy to correct a valgus deformity. Focal bone lysis was evident radiographically at the ostectomy site. Four months later, marked bony swelling was apparent and the dog was bearing partial weight. The dog was euthanatized, and at necropsy, a bone tumor with lung metastasis was found. Microscopically, features of the tumor were compatible with those of small-cell osteogenic sarcoma.