A 53-YEAR-OLD white woman was admitted to the hospital with a 3-day history of cough and dyspnea. Two years previously, a ductal carcinoma of the breast (already with widespread metastases) had been diagnosed. On this admission, significant arterial hypoxia was noted. The results of echocardiography showed right ventricular dilatation. An electron beam computed tomographic scan was interpreted as negative for pulmonary embolism. Despite the interpretation, the patient was diagnosed as having pulmonary thromboembolism and was given anticoagulant therapy. She died of progressive respiratory failure 2 weeks after admission to the hospital.