Malignant phyllodes tumours of the breast display increased stromal p53 protein expression

Aims: To determine the variation in p53 protein expression in phyllodes tum ours and fibroadenomas of the breast. Methods and results: Fifteen phyllodes tumours (six malignant, nine benign) and 20 fibroadenomas were examined for p53 expression by immunohistochemis try. Five of the six malignant phyllodes tumours showed moderate or strong p53 positivity at sites of peri-epithelial stromal condensation and atypia, All 20 fibroadenomas, nine benign phyllodes tumours and one malignant phyl lodes tumour showed either negativity or focal weak nuclear positivity of s cattered stromal cells. Conclusions: Increased p53 immunoreactivity is present in malignant phyllod es tumours in contrast to benign phyllodes tumours and fibroadenomas. Malig nant phyllodes tumours display a distinctive pattern of p53 immunostaining which may be of diagnostic value. These findings suggest that p53 protein m ay be important in the progression of benign to malignant phyllodes tumours .