What palliative and systemic treatment options exist for dogs with osteosarcoma when amputation is declined?

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When amputation is declined, palliative radiation therapy (RT) is the most effective local treatment for canine appendicular osteosarcoma (OSA), and systemic chemotherapy with carboplatin or doxorubicin is the standard adjuvant approach to address micrometastatic disease. Palliative RT provides meaningful pain control and is a recognized treatment option for dogs with OSA when surgery is not pursued. 12 The role of RT in this setting is analgesic and cytoreductive rather than curative, and it is typically combined with systemic chemotherapy to address the near-universal burden of occult metastatic disease. 26 Stereotactic RT (also called stereotactic body radiation therapy) is an established limb-sparing option that achieves local control with survival times comparable to amputation when combined with adjuvant chemotherapy, yielding a median survival time (MST) of approximately 10–12 months. 113 This is equivalent to the MST achieved with amputation plus chemotherapy (MST ~10–12 months), making it a legitimate alternative when owners decline amputation. 113 Carboplatin- or doxorubicin-based chemotherapy is the standard systemic treatment and is recommended regardless of the local control strategy chosen. 12 Adjuvant platinum-based chemotherapy, with or without alternating doxorubicin, extends MST from approximately 5 months (local treatment alone) to approximately 10–12 months. 1213 The 1-year survival rate with amputation and adjuvant chemotherapy is 45.5%, and the 2-year survival rate is 20.9%. 12 Without adjuvant chemotherapy, the 1-year survival rate drops to 19.8% and the 2-year rate to 2%. 12 These figures apply to the amputation-plus-chemotherapy cohort, but the chemotherapy survival benefit is attributed to systemic anti-metastatic effect and is expected to apply regardless of the local control method used. 613 Metronomic cyclophosphamide (15 mg/m² PO q24h) with concurrent NSAID administration has been evaluated as maintenance therapy following carboplatin c