The transcription factor erythroblastosis virus E26 transforming sequence related gene (ERG) functions as a regulator of key cellular functions to promote endothelial homeostasis.¹ Expression of ERG has been observed in both benign and malignant vascular endothelial tumors, such as hemangiomas and Kaposi sarcomas, respectively.^2,3 Carcinomas of the breast, colon, and urothelium have demonstrated absence of ERG expression, whereas presence of the protein has been confirmed in a subset of prostate carcinoma cases.^4,5 Anti-ERG can be a useful tool for identifying vascular endothelial neoplasms and distinguishing prostate carcinoma from epithelial tumors of non-prostatic origin.