The rate of mitosis in cystosarcoma phyllodes (phyllodes tumor, WHO) of the breast. An analysis of 47 cases.

The rate of mitosis was determined in 47 cases of cystosarcoma phyllodes which had already been classified by morphological criteria (tumor margin and cellular atypia) as benign (17 cases), malignant (23 cases) and borderline (7 cases). Tumors which had been classified histopathologically as benign or of borderline had mitotic rates of 3 mitosis/10 HPF or less, whereas malignant cystosarcomas showed rates of 2-36 mitoses/10 HPF. Only high rates of mitosis (10/10 HPF) correlated well with a histopathologic diagnosis of malignancy.