We read with interest the article entitled “Distant cutaneous metastases of prostate cancer: a report of 2 cases”1 in which an exhaustive immunohistochemical study left no doubt about the diagnosis. These cases remind us of usefulness of avian erythroblastosis virus E26 oncogene homolog (ERG) in the cutaneous diagnosis of prostate cancer metastasis.

ERG is a member of the erythroblast transformation-specific family of transcription factors. It is expressed in normal and neoplastic endothelial cells of blood and lymph vessels and is a highly specific marker of vascular endothelium. ERG is very useful in the diagnosis of angiosarcomas, hemangioendotheliomas, and Kaposi's sarcoma. However, it is also positive in the following cell types: 1) neoplastic epithelial cells of 50% of primary and metastatic prostate carcinomas (Figure 1), but not in normal prostate tissue; 2) immature myeloid cells in bone marrow; 3) chronic myeloid leukemia cells; and 4) Ewing sarcoma cells.2 The fact that it is positive in prostate carcinoma but negative in almost all other carcinomas makes ERG a very valuable in immunohistochemical panels used to investigate cutaneous metastases of unknown origin.3

Figure 1.

Subcutaneous nodule in right paravertebral back (ERG×200, nuclear staining).

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