Primary squamous cell carcinoma of the breast.

Upon reexamination of about 4000 breast cancer biopsies, three pure primary squamous cell carcinomas (SCC) were found. The light and electron microscopic findings of these three cases are described. The carcinomas seemed to originate from the glandular tissue of the breast and followed an extremely aggressive clinical course. SCC must be regarded as a separate entity distinct from adenocarcinoma of the breast with squamous cell metaplasia.