Objective: To assess the diagnosis of squamous cell carcinoma involving the breast by fine needle aspiration cytology in four cases (two primary and two metastatic).
Study design: All patients were women between the ages of 42 and 74 years. The aspiration findings were confirmed by cell blocks of the aspirates, biopsy and/or comparison of the tissue from the previous primary. The aspirate was obtained using multiple passes in the breast masses while maintaining negative pressure.
Results: The cytohistologic features in all cases were characterized by numerous malignant squamous cells with hyperchromatic, enlarged, dense nuclei; thickened nuclear membranes; coarse chromatin; abundant eosinophilic, keratinizing glassy cytoplasm; and a necrotizing background with keratin debris. The diagnostic value of immunocytochemical study was considered questionable despite immunopositivity for cytokeratin and epithelial membrane antigen and negative staining for carcinoembryonic antigen and B72.3 in all cases.
Conclusion: The identification of malignant squamous cells in breast aspirates is an important observation. Such cells, when seen as the predominant ones in an aspirate, should prompt a search for other sources of a primary tumor before a diagnosis of squamous cell carcinoma of the breast is accepted.