A 36-year-old woman with breast cancer was admitted with shortness of breath. A computed tomography angiogram was obtained and was negative for pulmonary embolism. She quickly developed hypoxemic respiratory failure and was transferred to the intensive care unit. She appeared to be improving when she suffered sudden cardiac death. Autopsy showed extensive lymphatic and vascular tumor emboli, which were the immediate cause of death. Tumor emboli are rarely diagnosed before death but seem to be more common than realized. It is important to recognize this entity, because there have been some case reports of cure. The usual mechanism of death is progressive right heart failure; sudden death from tumor embolism has rarely been described.