MYC amplification has been reported as a prominent feature of secondary angiosarcomas (SAS). The differential diagnosis between atypical vascular lesion (AVL) and low-grade angiosarcoma (AS) can be occasionally very difficult or even impossible, and MYC amplification status has been pointed as an important diagnostic tool to distinguish cutaneous vascular lesions of the breast. We assessed MYC amplification and protein expression status by fluorescent in situ hybridization (FISH) and immunohistochemistry (IHC), respectively, in 49 patients diagnosed with breast AS, and 30 patients diagnosed with post-radiation AVL of the breast. Clinical and pathological features, and follow-up data were collected, and survival analyses were performed. Among 37 patients with SAS, twenty patients had tumors with high-level MYC amplification and protein overexpression (54 %). None of primary angiosarcomas (PAS) or AVL cases showed MYC amplification or protein expression. Concordance between MYC amplification (FISH) and protein expression (IHC) was 100 % in AVL, PAS, and SAS. Survival analysis of the SAS patients demonstrates that those with MYC amplification had a significantly worse overall survival compared to cases without MYC amplification (P = 0.035). There was a non-significant trend toward a poor disease-free survival between cases with and without MYC amplification (P = 0.155). Our findings show that MYC amplification is a highly specific but poorly sensitive marker for SAS and, therefore, a negative result does not exclude the diagnosis of angiosarcoma. MYC amplification was associated with adverse prognosis, suggesting a prognostic role of MYC amplification status on SAS of the breast.