In a study of 40 dogs by Kyles, the short-term mortality rate was evaluated in regards to the presence of caval tumor thrombus. Reportedly, tumor thrombus was seen in 25% of all dogs. Eleven percent of adenocarcinomas had tumor thrombus and 55% of pheochromocytomas had tumor thrombus. As mentioned there was no difference in the perioperative death rate regardless of presence or absence of tumor thrombus. The perioperative death rate was 21% for adenocarcinomas and 18% for pheochromocytomas. Previously, pheochromocytomas patients have a high perioperative mortality rate, but the addition of protocols that include administration of high doses of phenoxybenzamine (as high as mg/kg twice daily) have reduced the death rate.