Fine needle aspiration cytopathology of phyllodes tumor. Differential diagnosis with fibroadenoma.

The differential diagnosis of benign or borderline phyllodes tumors of the breast in fine needle aspiration biopsy smears was studied. Smears from five histologically proven cases and 20 proven cases of fibroadenoma were evaluated with regard to their cytologic features. The findings indicate that the presence of a high cellularity of stromal fragments (including bipolar naked nuclei), clusters of hyperplastic ductal cells and giant cells and the absence of apocrine metaplasia may suggest a diagnosis of phyllodes tumor, as opposed to fibroadenoma. The borderline phyllodes tumor showed a sarcomatous atypia and/or small intranuclear cytoplasmic invaginations in some cells. The differential diagnosis of this tumor with malignant phyllodes tumor and plasma-cell mastitis is also discussed.