Extramammary Paget disease of the axilla associated with comedo-like apocrine carcinoma in situ

Extramammary Paget disease of the axilla with underlying apocrine carcinoma has been reported only in six cases until now. This report deals with a seventh case characterized by the unique finding of comedo-like features evocative of large cell ductal breast carcinoma within an otherwise typical in situ apocrine carcinoma. This is characterized by spiral-shaped foci of epithelial proliferation with decapitation secretion and central masses of necrotic debris. A possible connection between the solid neoplasm and the overlying Paget disease is illustrated by a few apocrine-follicular units colonized by both the Paget cells and the structured adenocarcinoma. Here, although they display the same immunohistologic pattern of glandular differentiation, the two populations seem to be cytologically different and do not show signs of gradual transition to one another. Thus, they give the impression of parallel but distinct processes, which is consistent with the hypothesis of proliferative induction of a preexisting intraepidermal scattered population from the underlying adnexal carcinoma. The observed resemblance between apocrine carcinoma and comedo carcinoma of the breast, with its ontogenetic and phylogenetic implications, links not only the two neoplasms and the corresponding glands of origin but also mammary and extramammary Paget disease. This reinforces the unifying conception of Paget disease.