Early Onset Post-Radiation Cutaneous Angiosarcoma of the Breast with Features of Atypical-Vascular Lesion: A Diagnostic Pitfall and Its Biologic Significance

Vascular proliferations may arise in the breast following radiation treatment for a primary breast adenocarcinoma. A post-radiation vascular proliferation can usually be classified as angiosarcoma or as an atypical vascular lesion (AVL). Angiosarcomas with a “low-grade ” morphology, behave ag-gressively but exhibit substantial histomorphologic overlap with AVLs, which have a generally be-nign clinical course. We present a case of a post-radiation angiosarcoma of the breast with histo-logic features that mimic an atypical vascular lesion and discuss this challenging differential di-agnosis. In addition to histologic mimicry, the lesion exhibited only patchy amplification of the avian myelocytomatosis viral oncogene homolog (MYC) gene by present fluorescence in-situ hy-bridization (FISH), and patchy MYC overexpression by immunohistochemistry. These features fur-ther complicate the distinction between AVL and angiosarcoma, and would be particularly prob-lematic on a small biopsy. We believe that the morphologic and immunohistochemical overla