A 2.5-year-old male castrated Newfoundland presented to his referring veterinarian for evaluation of a acute onset of difficulty ambulating and an approximately 5-7cm mass over the left lateral stifle that had arisen over the past 48 hours. Radiographs showed a massive soft-tissue opacity surrounding the stifle of the left leg, including bony lysis and irregular cortical margins extending from just distal to the patella to the mid-tibia. Cytology of the mass yielded spindle-shaped cells; histopathology of the incompletely excised tumor showed a high-grade fibrosarcoma. When referred to the Oncology Service at the Cornell University Hospital for Animals (CUHA) for further treatment, the dog was staged: three-view thoracic radiographs, abdominal ultrasound and cytology of a regional lymph node showed no evidence of metastasis. Options for treatment including amputation and chemotherapy were discussed, but the owners elected to pursue definitive radiation treatment given concerns over mobility post coxofemoral disarticulation. This paper describes the course of the dog's multimodal treatment at Cornell and other practices, including amputation and complementary approaches such as palliative physical therapy and acupuncture.