Prostein (p501s) is expressed in primary extramammary Paget disease

AIMS: Extramammary Paget disease (EMPD) is an intraepidermal carcinoma that typically involves the urogenital, perineal and perianal skin. EMPD is classified as primary if arising directly in the skin, or secondary if spreading from another malignancy, most commonly urothelial carcinoma and colorectal adenocarcinoma. Prostein (p501s) immunoreactivity was initially described as sensitive and specific for prostatic epithelial cells including prostatic adenocarcinoma. Herein, we investigated the expression of prostein in primary EMPD of the external genitalia, secondary EMPD involving the external genitalia or perineum, and mammary Paget disease (MPD). METHODS AND RESULTS: Prostein was negative by immunohistochemistry in all cases of MPD (n = 0/11) and secondary EMPD (n = 0/5). Conversely, prostein was positive in all cases of primary EMPD (n = 11/11), including non-invasive and invasive components and including one nodal metastasis. Among these cases, 5/11 (45%) showed non-focal moderate-to-strong staining, 3/11 (27%) showed focal weak staining, and 3/11 (27%) cases showed weak diffuse staining. All cases of primary EMPD additionally showed diffuse 2-3+ staining for GATA3, and 10/11 cases of primary EMPD showed diffuse 2-3+ staining for androgen receptor (AR). CONCLUSIONS: These findings suggest that prostein may be a promising immunohistochemical marker for the diagnosis of primary EMPD.