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Background:  While cytokeratin 7 is a reliable marker for most cases of Paget’s disease, it is not 100% sensitive. Moreover, cases of cytokeratin 7-positive pagetoid squamous cell carcinoma in situ are reported in the literature. The monoclonal antibody Ber-EP4 is diagnostically highly reliable in the differentiation between basal cell carcinoma and cutaneous squamous cell carcinoma. Here we report its application in the differential diagnosis of cutaneous pagetoid neoplasms.

Methods:  Biopsy samples from 21 cases of extramammary Paget’s disease, 12 pagetoid squamous cell carcinomas in situ and 10 pagetoid melanomas in situ of the superficial spreading type were examined immunohistochemically with Ber-EP4, 34βE12 and HMB-45.

Results:  Ber-EP4 selectively labeled all cases of extramammary Paget’s disease but none of the other pagetoid neoplasms. The majority of cases (18 = 85.7%) displayed strong and three (14.3%) showed moderate immunoreactivity.

Conclusions:  Ber-EP4 reliably differentiates extramammary Paget’s disease from pagetoid squamous cell carcinoma in situ and pagetoid melanoma in situ. The antibody should be included along with a panel of other markers when evaluating for pagetoid cutaneous neoplasms in order to avoid a possible misdiagnosis of pagetoid squamous cell carcinoma in situ.