Cytokeratin 7-negative mammary Paget's disease: A diagnostic pitfall.

Pathologists should be aware of the existence of a rare CK7-negative variant of breast carcinoma in general, and of Paget's disease in particular. Cytokeratin 7-negative Paget's disease and CK7-negative ductal intraepithelial neoplasia (ductal carcinoma in situ) present a major diagnostic challenge for pathologists since there is limited awareness of their existence. When there is classic Paget's morphology on H&E sections, GATA3 positivity should resolve any doubts about the diagnosis in the setting of a CK7-negative neoplastic cell population.