A case of malignant phyllodes tumor that responded to pazopanib and developed pneumothorax.

Here, we present a 59-year-old female with recurrent malignant phyllodes tumor with multiple lung and lymph node metastases who developed a pneumothorax after the administration of pazopanib. The patient received pazopanib as the second-line chemotherapy. After 2.5 months of the therapy, computed tomography (CT) showed a decrease in the sizes and cavitation of lung lesions; however, a left pneumothorax was newly observed. It was difficult to distinguish the pneumothorax by upright chest X-ray. Typical symptom or physical finding of pneumothorax, such as dyspnea, chest pain or decreased breath sound was not observed. As the pneumothorax was small and asymptomatic, the administration of pazopanib was discontinued and follow-up chest X-ray and CT were performed. After 1 week, CT showed an improvement in the pneumothorax. Chemotherapy was switched to eribulin; however, a rapid increase in sizes of lung lesions was observed after the first administration of eribulin, pazopanib was reintroduced. Careful follow-up by chest X-ray and CT was performed and the pneumothorax has not recurred.