Fine needle aspiration cytologic features of mammary phyllodes tumors

OBJECTIVE: To evaluate specific diagnostic fine needle aspiration cytologic (FNAC) features of phyllodes tumor (PT), particularly in the differentiation from fibroadenoma (FA). STUDY DESIGN: Twenty-eight FNAC of PT were reviewed for smear cellularity, epithelial and stromal fragments, their size and atypia, epithelial/stromal area ratio, background single stromal cells (oval or columnar), multinucleated giant cells, and squamous and apocrine cells. Twenty-one FNAC of fibroadenoma were also assessed for comparison. RESULTS: PT was significantly larger than FA. Epithelial fragments were found in all cases, with atypia present in PT. Stromal fragments were present in half the cases; there was no difference in stromal size, but the epithelial/stromal area ratio was significantly lower in PT than FA. Single columnar stromal cells with recognizable cytoplasm and multinucleated stromal giant cells were seen in some PT but not in FA. CONCLUSION: Cytologic diagnosis of PT remains difficult, with significant overlap with FA. The presence of large size, low epithelial/stromal ratio, epithelial atypia, columnar stromal cells with visible cytoplasm and stromal giant cells favors a diagnosis of PT over FA.