Microsatellite-Stable Radiation-Induced Angiosarcoma after Breast-Conserving Surgery: A Case Report.

Radiation-induced angiosarcoma (RIAS) after breast-conserving surgery is quite rare. Risk factors for RIAS have yet to be identified, due largely to the very low incidence of this disease. The etiologic mechanisms of RIAS are not understood, although some reports suggest that genome instability may contribute to RIAS development. An 81-year-old Japanese woman presented to our hospital after developing multiple dark purple nodules on her left breast. She had undergone breast-conserving surgery for left breast cancer and adjuvant radiotherapy for the conserved breast 9 years earlier. Punch biopsy of one of the dark purple nodules was performed and the pathological diagnosis was angiosarcoma. She underwent total mastectomy with an adequate margin, and skin collected from her left thigh was grafted onto the site. Pathologically, the surgical margin was negative. The tumor was negative for microsatellite instability (MSI). Considering her age, she has remained under careful observation with neither systemic treatment nor adjuvant radiation. The only standard therapy for RIAS currently available is complete resection. Hence, early detection is crucial to obtain an adequate margin, followed by careful observation after breast-conserving surgery. It is also essential to reveal the tumor etiology, and for that purpose, we believe that the MSI status may be beneficial for the further investigation of RIAS.