Abstract Osteosarcoma (OSA) is the most common and aggressive primary bone tumor in dogs. OSA frequently metastasizes to the lungs and has a poor prognosis despite current standard treatment. This case report described the clinical course of a 3-year-old castrated male Jindo dog diagnosed with right tibial OSA and a pre-existing pulmonary metastasis. Initially, the patient received adjuvant chemotherapy and maintained a stable disease state for several months until radiographic and computed tomography (CT) examinations revealed progressive pulmonary metastasis. In response to this progression, combination therapy with high-dose losartan (angiotensin II type 1 receptor blocker ARB, 10 mg/kg PO SID) and toceranib (2.75 mg/kg PO EOD) was initiated concurrently with ongoing carboplatin cycles. Two months after initiating this new regimen, a comprehensive CT re-evaluation demonstrated a significant positive response, marked by the radiographic disappearance of pulmonary nodules and complete resolution of the pleural effusion. This substantial improvement indicated a potential synergistic anticancer effect, likely mediated by losartan's capacity to remodel the tumor microenvironment (TME), suggesting a likely niche therapy, thereby enhancing toceranib efficacy. Despite this initial success, the patient’s condition ultimately deteriorated after the completion of chemotherapy, confirming extensive disease progression. A subsequent attempt with doxorubicin as a third-line agent resulted in severe adverse effects, such as bone marrow suppression and neutropenia, leading to the patient's death shortly thereafter (Table 1). This case contributed compelling clinical evidence of the promising short-term efficacy of high-dose losartan in combination with toceranib for progressive pulmonary metastatic OSA, potentially through favorable TME modulation. It also highlighted the inherent virulence of canine OSA and the challenges in achieving sustained long-term control. The development of innovative multimodal therapeutic approaches for the management of canine OSA is critically important.
Kwak et al. (Mon,) studied this question.