Objective: To elucidate the fine needle aspiration cytology (FNAC) features of phyllodes tumor (PT).
Study design: Eight FNAC cases of PT (five benign and three malignant) were reviewed. Features examined were cellularity, epithelial/stromal ratio, phyllodes fragments (PFs), blood vessels crossing PFs, bipolar naked nuclei, stromal pleomorphism, stromal cell size, mitosis, macrophages, sarcomatous component and atypical epithelial component.
Results: Benign PTs were characterized by cellular smears with both stromal and epithelial elements. All cases had many highly cellular stromal fragment PFs. Stromal cells were twice the size of a lymphocyte and lacked pleomorphism. Bipolar naked nuclei were a constant feature. The epithelial component predominated, demonstrating benign ductal groups and cellular areas with discohesion superficially mimicking adenocarcinoma in three cases. FNAC of primary malignant PT (one case) had two patterns, one mimicking benign PT and the other demonstrating a pure sarcomatous component. FNAC of metastatic PTs (two cases) showed pure sarcomatous elements.
Conclusion: The diagnosis of PT is favored over fibroadenoma when many PFs are present. The size and shape of the stromal cell nuclei were not helpful differentiating features in this study. The diagnosis of malignant PT was based on the purely sarcomatous component.