Case of Radiation-Induced Angiosarcoma after Breast-Conserving Surgery with Hypofractionated Radiotherapy in a Japanese Patient

Radiation-induced angiosarcoma (RIAS) is a rare, late adverse event of radiotherapy comprising approximately half of all radiation-induced sarcomas. It has a relatively short latency period and generally unfavorable prognosis. This study presents a case of RIAS that developed 5 years and 11 months after the completion of hypofractionated radiotherapy (42.56 Gy/16 fractions) following partial mastectomy. The patient was diagnosed with RIAS 10 months after the onset of skin redness. She underwent skin tumor resection, followed by paclitaxel, then pazopanib administration, but no radiotherapy. At 6 years and 2 months after surgery, no RIAS recurrence has been detected.