Toceranib phosphate resolves right heart obstruction secondary to a heart base neoplasm in a dog

An eight-year-old castrated male, 45 kg labrador retriever presented for evaluation of a two-week history of cough and tachypnoea. Echocardiography revealed an approximately 10 cm heart base mass, which extended to the right atrioventricular junction, causing compression of both the right atrium and ventricle resulting in right-sided congestive heart failure (abdominal effusion). Cytology of the mass was consistent with a neuroendocrine carcinoma. Given the location and description, a chemodectoma or ectopic thyroid carcinoma was suspected. The patient was treated with toceranib phosphate and famotidine. At the follow-up appointment four weeks later, the right heart compression had resolved due to a clinically significant reduction in the size of the mass. The patient was prescribed furosemide and enalapril to treat right-sided congestive heart failure. When considering treatment options for haemodynamically significant heart base masses, treatment with toceranib phosphate may result in rapid clinical benefit.