Ductal eccrine carcinoma presenting as a Paget's disease-like lesion of the breast

Some types of skin appendage tumors, particularly ductal eccrine carcinomas (DEC), imitate breast carcinomas histologically, thus causing great diagnostic challenges. We describe a case of DEC presenting as an eczematous, crusted skin lesion on the right nipple-areolar complex in a 67-year-old woman. A skin biopsy done under the clinical impression of Paget's disease of the nipple was initially misinterpreted as infiltrating ductal carcinoma, and a subsequent modified radical mastectomy revealed DEC exclusively confined to the nipple with perinodal tumor metastasis in one of the axillary lymph nodes. This case highlights the diagnostic difficulty caused by the histologic homology between breast carcinomas and skin appendage tumors with ductal differentiation.