Abstract. Pulmonary artery sarcoma (PAS) is a rare and highly malignant tumor of pulmonary artery origin. Since 1923, when the first case was reported, <300 cases have been reported worldwide. PAS has a poor prognosis, and early diagnosis with radical surgical resection offers patients with PAS the only chance of survival. However, due to its rarity and the non-specificity of its clinical manifestations and imaging presentation, PAS is frequently misdiagnosed as a pulmonary thromboembolic disease, including pulmonary thromboembolism (PTE) and chronic thromboembolic pulmonary hypertension (CTEPH). The present study reports three cases of PAS that were initially misdiagnosed as PTE or CTEPH, and were later shown to be PAS following surgery. In addition, the clinical features of these patients are examined in order to improve the differential diagnosis of PAS during the early stages of the disease, when the prognosis of patients with PAS is at its optimum. IntroductionPulmonary artery sarcoma (PAS) is a rare malignant tumor originating from the pulmonary blood vessels (1). Since it was initially reported by Mandelstamm (2) in 1923, <300 cases have been reported in the literature (3,4). Clinically, PAS can easily be misdiagnosed as a pulmonary thromboembolic disease, such as pulmonary thromboembolism (PTE) or chronic thromboembolic pulmonary hypertension (CTEPH) (5-7). In such instances, patients lose the opportunity for early diagnosis and treatment (8,9). In the present study, the clinical data of three patients with PAS, as confirmed by surgery at the Beijing Anzhen Hospital (Beijing, China), are reported and analyzed, in order to raise awareness and improve the diagnosis of PAS. Case reportCase 1: Female patient, 36 years old. The patient was hospitalized on the 26th October 2008 having experienced shortness of breath and chest tightness for 50 days and four syncopes. In September 2007, the patient had suddenly fainted during agricultural work and had experienced loss of consciousness and incontinence for ~10 min; however, no abnormalities were detected by the local hospital upon waking. Thereafter, the patient experienced recurrent shortness of breath, chest tightness and difficulty breathing, and discontinuous syncopes occurred three times in the absence of chest pain, hemoptysis and convulsions. A chest X-ray obtained from a local hospital showed no abnormalities, although a chest computed tomography pulmonary angiography (CTPA) performed in September 2007 showed a suspected pulmonary embolism. The patient was transferred to the Beijing Anzhen Hospital to confirm the diagnosis and provide effective treatment. Prior to these events, the patient had been healthy, with no history of a rash, joint pain, lower extremity swelling or trauma surgery, and no history of oral contraceptive use.The results of a physical examination were as follows: Blood pressure (Bp), 110/66 mmHg (normal range, 90-140/60-90 mmHg); respiratory rate (R), 20 times/min (normal range, 16-20 times/min); and heart rate (HR), 79 beats/min (norm...