Cystosarcoma phyllodes. A clinicopathologic study of twenty-six hypercellular periductal stromal tumors of the breast

A series of 26 hypercellular periductal stromal tumors of the breast, commonly referred to as cystosarcoma phyllodes, is reported. Twelve neoplasms were classified histologically as benign and 14 (54%) as maligant after microscopic assessment of the stromal elements. None of the histologically benign cystosarcomas metastasized, although two recurred locally. Malignant transformation was not observed in the recurrent tumors. Local recurrences developed in four women with histologically malignant cystosarcomas and caused the death of one by direct extension into the lung. Pulmonary metastases of the sarcomatous element occurred in three. Two of these women died and one has survived 16 years after pulmonary lobectomy. Separation of cystosarcomas into benign and malignant categories on the basis of their histopathologic features is advocated. It is likely that overgrowth of the sarcomatous stroma is a prerequisite for metastasis.