Case summary A 12-year-old male neutered Bengal cat presented for a left thoracic limb lameness of several weeks’ duration. Abnormal advanced imaging findings depicted the presence of an irregularly marginated osteolytic lesion in the proximal-mid diaphysis of the left humerus. A histopathological evaluation of the humerus confirmed a diagnosis of osteoblastic osteosarcoma. Limb-sparing surgery was planned with a custom-designed three-dimensional printed endoprosthesis. Mild neuropraxia was noted immediately postoperatively and deemed to have resolved by the 2-week follow-up. Stereotactic radiation was planned, though pulmonary metastasis was noted on planning CT. The cat was euthanased 90 days postoperatively owing to the development of pulmonary clinical signs.

Relevance and novel information This is the first reported case of a humeral limb salvage procedure in a cat using a custom-designed three-dimensional printed endoprosthesis. Although the survival time in this case was short, the patient maintained an adequate quality of life and limb function was preserved.