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 aggressively but exhibit substantial histomorphologic overlap with AVLs, which have a generally benign clinical course. We present a case of a post-radiation angiosarcoma of the breast with histologic features that mimic an atypical vascular lesion and discuss this challenging differential diagnosis. 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 hybridization (FISH), and patchy MYC overexpression by immunohistochemistry. These features further complicate the distinction between AVL and angiosarcoma, and would be particularly problematic on a small biopsy. We believe that the morphologic and immunohistochemical overlap between these entities is suggestive of a biologic spectrum, and thus that, at least in some instances, angiosarcoma may arise from a pre-existing AVL or AVL-like lesion.