RESUMO
Pigmented extramammary Paget's disease (PEMPD) is an uncommon intraepithelial adenocarcinoma and a rare variant of Paget's disease affecting skin that is rich in apocrine sweat glands such as the axilla, perianal region and vulva. It most commonly occurs in postmenopausal women and presents as a superficial pigmented scaly macule, mimicking a melanocytic lesion. The histological presentation is adenocarcinoma in situ with an increased number of melanocytes scattered between the Paget's cells. Therefore, PEMPD may be misdiagnosed as a melanocytic tumour both clinically and histologically. The tumour cells are usually positive for cytokeratin 7, epithelial membrane antigen, Cam 5.2, HER2, and mucicarmine stain while S100 and human melanoma black-45 highlight the processes of reactive dendritic cells. The association between Paget's cells and intratumoural reactive melanocytes is still unclear. We report our first case of PEMPD associated with an intradermal naevus involving the axilla in a 63-year-old woman.