Expression of p53 protein and Ki-67 antigen in phyllodes tumor of the breast.

BACKGROUND Phyllodes tumors (PT) of the breast are uncommon, and it is often difficult to predict their clinical behavior from histologic features in individual cases. In addition to routine morphology, the studies of p53 protein and Ki-67 antigen expression in PT may be useful to differentiate benign from malignant tumors. METHODS Immunohistochemical analyses using monoclonal antibody to label p53 protein and another monoclonal antibody MIB-1 to label Ki-67 antigen were performed on the tissue sections of 63 PT from 56 patients. The percentages of positive staining tumor cells were compared with the tumor gradings and clinical outcomes. RESULTS According to histologic criteria, this series contained 50 benign and 13 malignant tumors. The p53 protein expression showed a significant difference between benign and malignant lesions. Within the group of benign lesions, 5 out of 50 (10%) tumors had p53 expression > 10%, whereas nine out of 13 (69%) malignant tumors revealed p53 expression > 10% (p < 0.005). The Ki-67 antigen was also well correlated with tumor grading. Eleven out of 13 (85%) malignant tumors but only 8 out of 50 (16%) benign tumors showed Ki-67 antigen increased > 10% (p < 0.005). Three patients progressed from benign to malignant tumors. All the first and recurrent tumors in these 3 patient showed Ki-67 > 10%. CONCLUSIONS P53 protein and Ki-67 antigen expression are correlated with the histology grading. In tumors with benign morphology but having a Ki-67 antigen > 10%, it is necessary to treat the patient and follow up properly to avoid recurrence and malignant transformation.