FISH for MYC amplification and anti-MYC immunohistochemistry: useful diagnostic tools in the assessment of secondary angiosarcoma and atypical vascular proliferations

Background: Secondary angiosarcoma and benign but microscopically atypical vascular proliferations (herein referred to as atypical vascular lesion or AVL) are rare consequences of radiation therapy and/or chronic lymphedema most commonly seen in breast cancer patients. Differentiating angiosarcoma from AVL can be difficult due to overlapping clinical and microscopic features. Recently, amplification of MYC has been associated with 55100% of secondary angiosarcomas but is reportedly absent in AVL. We examined a series of secondary angiosarcoma and AVL for MYC amplification by fluorescence in situ hybridization (FISH) and expression by immunohistochemistry to investigate the diagnostic utility for discriminating angiosarcoma from AVL. Methods: Cases of secondary angiosarcoma (n = 8) and AVL (n = 4) were retrieved from our archives and examined by FISH and immunohistochemistry. Results: All angiosarcoma cases (8/8 = 100%) demonstrated high- level MYC amplification by FISH, whereas all AVLs (0/4 = 0%) were negative for MYC amplification. Additionally, all angiosarcoma cases (8/8 = 100%) demonstrated nuclear positivity for MYC, whereas all AVLs (0/4 = 0%) were negative. Conclusion: Amplification of MYC and nuclear expression of MYC is present in secondary angiosarcoma but not AVL. These ancillary tests can be useful to distinguish angiosarcoma from AVL in difficult cases.