Primary squamous-cell carcinoma of the breast. Diagnosis by fine needle aspiration cytology.

A primary squamous-cell carcinoma of the breast was evaluated by fine needle aspiration cytology in a 41-year-old female. The subsequent mastectomy specimen contained a well-differentiated keratinizing squamous-cell carcinoma. On electron microscopic evaluation, the tumor cells contained well-formed desmosomes and prominent bundles of tonofilaments, typical of squamous-cell carcinoma in other organs. Thorough evaluation of the patient did not reveal squamous-cell carcinoma elsewhere.