Background: Extramammary Paget's disease (EMPD) remains a rare condition with only a limited number of cases reported in the literature. EMPD is mainly composed of intraepidermal Paget cells, and possesses variable clinical behaviors and histological appearances, leading to difficulty in the diagnosis of this disease.
Case presentation: We here report a case of primary EMPD with the appearance of a nodule on the background of erythema. Histological assessment showed Paget cell infiltration throughout the epidermis with dermal spread. Using immunohistochemistry, the expressions of CK7, CK19, CK20, GCDFP-15, CEA, S-100 protein and bcl-2 were examined to elucidate the cellular differentiation of the carcinoma.
Conclusion: According to the histological assessment, this case was diagnosed as primary EMPD with carcinoma cells invading into the dermis, but without lymph node infiltration.