Radiation-associated angiosarcoma in the setting of breast cancer mimicking radiation dermatitis: A diagnostic pitfall

BackgroundWe have encountered cases of post-radiation angiosarcoma (PRAS) histologically mimicking radiation dermatitis. MethodsCases of PRAS from institutional/consultation archives from 2006 to 2016 were reviewed. For inclusion, tumors had to have inapparent/subtle tumor at low magnification and scattered individual tumor cells resembling radiation fibroblasts. Prior ancillary studies were reviewed, with additional immunostains performed as needed. Results10 cases met criteria. All occurred in women treated for breast cancer (mean age 71 years). All had similar findings: in particular, scattered single atypical cells with pleomorphic nuclei associated with microscopic hemorrhage. They also had narrow, slightly wavy worm-like vascular channels lined by atypical endothelial cells that lacked architectural complexity. Four cases showed focal areas of more conventional angiosarcoma. One case was an excision of a large mass that showed the radiation dermatitis-like pattern radiating out from the central mass. All were positive for vascular markers (CD31, CD34, and/or ERG) and MYC. MYC amplification was demonstrated by FISH in both cases tested. In 3 of 3 cases with available re-excision specimens, more obvious angiosarcoma was seen. Conclusions PRAS can be very subtle and histologically mimic radiation dermatitis. Careful attention to histologic features and ancillary tests allow accurate diagnosis in subtle PRAS.