Atypical Non-neoplastic Changes in Anogenital Mammary-like Glands Accompanying Invasive Squamous Cell Carcinoma

Long regarded as ectopic or supernumerary breast tissue, anogenital mammary-like glands (AGMLG) are now considered a normal constituent of the anogenital area. AGMLG are presumed to be the origin for various benign and malignant lesions. Changes in AGMLG compatible with usual ductal hyperplasia and atypical ductal hyperplasia considered as precursor lesions and its presence in specimens can be explained by their role in the pathogenesis of primary extramammary Paget disease. In this report, we presented four cases of invasive squamous cell carcinoma accompanied by non-neoplastic atypical changes in ductal portions of AGMLG compatible with atypical ductal hyperplasia in breast adjacent to the carcinoma. This is a reactive phenomenon similar to that seen in apocrine/eccrine glands adjacent to squamous cell carcinoma. In a limited biopsy specimen, these areas should not be mistaken for adenocarcinoma.