The MYC proto-oncogene (bHLH transcription factor, a.k.a. CMYC) is located in the chromosomal region 8q24.21 and encodes a transcription factor that can activate and repress transcription thereby regulating expression of numerous target genes that are essential for cell growth and proliferation. Deregulation of MYC is a common denominator in cancer. MYC amplification was found e.g. in breast, colon, kidney, lung, ovary, bladder, head and neck, and endometrial cancer. Several studies showed a correlation between gene amplification and disease progression or recurrence in breast cancer and other malignancies. Malignant cutaneous angiosarcomas, for example, but not benign and atypical vascular lesions occurring after radiotherapy of breast cancer are characterized by amplification of the MYC gene. The presence of MYC amplification is thus of considerable diagnostic importance for the distinction of malignant from atypical postradiation vascular neoplasms of the skin. Since inactivation of MYC appears to be effective in the treatment of neoplasia MYC targeting therapies have been developed some of which have entered clinical trials.