Complete Remission of Metastatic Osteosarcoma From a Breast Malignant Phyllodes Tumor: A Case Report

Phyllodes tumors (PTs) are biphasic fibroepithelial lesions. Approximately 20% of malignant PTs metastasize hematogenously, most commonly to the lungs and bones. Treatment of metastatic PT is challenging because of its rarity. A 39-year-old woman with a left humeral fracture was admitted to our hospital. She had been diagnosed with breast PT a year prior, and humeral bone tissue pathology showed a metastatic PT similar to her breast PT. The patient received systemic high-dose chemotherapy, including etoposide, ifosfamide, and cisplatin, concurrently combined with radiotherapy to facilitate remission, after which the remnant tumor was removed. After achieving complete remission, the patient received chemotherapy with doxorubicin and cisplatin as adjuvants. To the best of our knowledge, this is the first report of a metastatic PT in which complete remission was achieved with high-dose chemotherapy combined with radiotherapy, followed by surgical resection and adjuvant chemotherapy.