A 10-year-old, spayed, female Cocker Spaniel was referred to our hospital with a history of a cough and dyspnea. The patient was tentatively diagnosed with a chemodectoma based on clinical features evident on echocardiography and computed tomography. Metronomic chemotherapy utilizing toceranib phosphate as well as medications for congestive heart failure were administered. During the period chemotherapy was administered (nine months from the time of diagnosis), clinical improvement was noted without the development of any adverse effects. However, clinical signs recurred after chemotherapy was discontinued at the owner’s request. When the patient was reevaluated via computed tomography, it was found that the size of the mass had increased. The patient developed severe dyspnea secondary to recurrent pleural effusion and was euthanized 65 days after clinical signs reappeared. A necropsy was performed and the patient was definitively diagnosed with a chemodectoma based on histopathologic and immunohistochemical analysis. This case report describes the clinical application of metronomic chemotherapy with toceranib phosphate, which is a tyrosine kinase inhibitor, in the treatment of a chemodectoma. We propose that this treatment may improve the quality of life and result in a prolonged survival time compared to treatment with medications for congestive heart failure alone.

Keywords: chemodectoma, metronomic chemotherapy, toceranib phosphate, tyrosine kinase inhibitor