Cystosarcoma phyllodes. Diagnosis by fine needle aspiration cytology.

The cytologic features of 10 benign, 2 borderline and 5 malignant phyllodes tumors were studied, and an attempt was made to correlate the cytologic findings with corresponding histologic categories. Seventy-five percent of the benign and borderline tumors were interpreted as benign cystosarcoma phyllodes on fine needle aspiration cytology. Eighty percent of the malignant phyllodes tumors were identified as malignant lesions cytologically. The cytologic features assessed were the epithelial:stromal ratio and morphology of the stromal component, including the degree of atypia, mitotic activity, capillary vessels traversing the stromal fragments, presence of foamy macrophages, histiocytic giant cells and bipolar naked nuclei. A diagnosis of phyllodes tumor was suggested cytologically by the presence of both epithelial and stromal elements; the stroma was present as cellular "phyllodes fragments" and isolated mesenchymal cells. The parameters suggesting malignancy were extreme paucity or absence of epithelial elements and stromal cells in diffuse sheets and clusters less cohesive than normal, with marked stromal atypia and mitotic activity.