Immunohistochemical Phenotypes of Phyllodes Tumor of the Breast

ABSTRACT

BACKGROUND: The aim of the study is to evaluate the difference of immunophenotypes of stromal cells between the pure phyllodes tumor (PT) type and the co-existent type of phyllodes tumor and fibroadenoma, and between benign and malignant PT. METHODS: Immunohistochemical staining for actin, CD34, CD10, c-kit, bcl-2, p53 and MIB-1 was performed using tissue microarray blocks that contained 25 cases of pure PT (16 benign tumors, 4, borderline malignant tumors, and 5 malignant tumors) and 6 cases of co-existent type. RESULTS: The expression rates of CD34 and MIB-1 in the pure PT type were significantly higher and the expression rate of actin in the pure PT was significantly lower than that of the co-existent type. However, there were no significant differences in the bcl-2, CD10, and p53 expressions between the pure PT type and the co-existent type, and no c-kit expression was observed in both types. No significant differences in the CD34, actin, bcl-2, CD10, and p53 expressions between the benign and borderline/malignant PT cases were found. However, a significant difference of the MIB-1 expression rate was noted. CONCLUSIONS: The stromal cells of the pure PT type are regarded as less mature myofibroblasts, and the CD10 reactivity in some phyllodes tumors suggests a myoepithelial origin. The MIB-1 labeling index would be useful for the grading of phyllodes tumor.