Late-onset osteosarcoma after onychectomy in a cat

CASE SUMMARY: A 12-year-old neutered male onychectomized Ragdoll cat presented for a 3 day history of swelling and hemorrhagic purulent discharge on the first digit of the left manus. Radiographs revealed fragments of the third phalangeal bone (P3) present in the partially amputated digits with swelling adjacent to the P3 fragment on the first digit of the left manus. Thoracic radiographs revealed no evidence of primary or metastatic neoplasia. Surgery was performed to remove all P3 fragments and the associated swelling on the diseased digit. On gross examination of the excised swelling, a mass was present at the cut edge of P3. The bone fragment and associated mass were submitted for histopathological evaluation. Osteosarcoma was diagnosed. Because neoplastic cells extended to the surgical margins, amputation of the left thoracic limb was performed. The cat recovered from surgery, and survival time at the time of writing was 8 months. RELEVANCE AND NOVEL INFORMATION: To our knowledge, this is the first reported case of onychectomy-associated osteosarcoma. Trauma from partial P3 amputation during onychectomy is suspected to have played a role in osteosarcoma development in this case. Malignant transformation may be considered a potential complication of onychectomy achieved by partial P3 amputation.