CD10, actin, and vimentin expression in breast phyllodes tumors correlates with tumor grades of the WHO grading system.

The discrimination of borderline from malignant primary breast phyllodes (PT) tumor is still unclear. We studied 22 PT cases to investigate the immunohistochemical expression (staining of stromal CD10, SMA [smooth muscle actin], and vimentin) as well as the features of focal glandular atypia to determine whether these correlated with the histopathologic grading system. In our results, the stromal staining of CD10 was positive in 4 of 6 malignant and 2 of 5 borderline PT cases, but negative in all benign PT cases. Stromal actin and intraglandular vimentin-expressive tumor cells were found in 5 of 6 malignant PT cases but not in borderline and benign PT cases. There is a significant difference in the panel of stromal CD10, actin, and vimentin expression between borderline and malignant PT (p<0.05). Besides, the progression of malignant potential breast phyllodes tumor may cause glandular epithelium atypia with loss of polarity.