Fine needle aspiration cytology of squamous cell carcinoma of the breast

A rare case of pure squamous cell carcinoma of the breast is reported in which the diagnosis was initially suggested by fine needle aspiration cytology. Smears and cell blocks of the aspirate showed atypical keratinized cells admixed with inflammatory cells. The diagnosis was confirmed by open biopsy. The excised tumor tissue was positive for both estrogen and progesterone receptors; flow cytometry showed a diploid DNA content and a high S-phase fraction.