Cytologic evaluation of phyllodes tumors as compared to fibroadenomas of the breast.

In an attempt to better understand the cytopathologic features of phyllodes tumors (PTs) and to differentiate PTs from fibroadenomas (FAs) of the breast, cytologic smears prepared from 17 and 19 histologically diagnosed cases of PT and FA, respectively, were reviewed. PT cases were histopathologically graded as benign, borderline and malignant. Cytologically, hypercellularity of stromal cells with recognizable cytoplasm was observed in 6 of 7 borderline and malignant PT cases, but none of the benign PT or FA cases revealed such hypercellular stroma. Between all PT and FA cases, no statistically significant differences could be obtained in the nuclear size of stromal cells, folding of epithelial cell sheets or number of foamy macrophages. The study revealed that the abundance of stromal cells with cytoplasm, not naked nuclei, was strongly suggestive of borderline and malignant PT, but the differentiation between benign PT and FA was difficult on the basis of the cytopathologic findings.