Undifferentiated malignant neoplasms, which occur primarily in the pulmonary artery, are extremely rare and associated with poor outcomes as there is no effective therapy. A 67-year-old woman visited our hospital with complaints of dry cough and dyspnea on exertion. A contrast-enhanced chest computed tomography revealed an intravascular tumor obstructing the left pulmonary artery and a pedunculated lesion extending to the main and right pulmonary artery. Multiple metastases in the lung, bones and bilateral adrenal glands were identified by fluorodeoxyglucose-positron emission tomography. A small sample was obtained by catheter aspiration biopsy of the intravascular tumor, and examination revealed undifferentiated small atypical cells. The tumor was diagnosed as an undifferentiated neoplasm arising from the pulmonary artery based on immunohistochemical findings, including the absence of expressions of organ-specific markers. Systemic chemotherapy (paclitaxel and carboplatin) and concurrent radiation were performed as treatment for the primary tumor. Marked shrinkage of the intravascular tumor was achieved, and no serious adverse events were observed during therapy. Chemotherapy was continued for 5 months, but the patient died because of tumor progression 9 months after the initial diagnosis. Chemoradiotherapy has efficacy against undifferentiated neoplasm of the pulmonary artery.
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