[Malignant metastasizing cystosarcoma phylloides of the breast. Ulm collection of rare tumors: VI].

Malignant cystosarcoma phylloides represents the malignant form of mammary fibroadenoma. In spite of atypical epithelial components, the biological behaviour of the tumour depends on malignant transformation of the dominant mesenchymal stromal tissue in the tumour. The histological appearance, often extremely variable, usually corresponds to a fibrosarcoma. Lipoblastic, chondroid and myxoid structures or areas of ossification may be present, although a completely dedifferentiated cystosarcoma is rare. The epithelial structures which are typically canalicular may reveal hyperplastic and dysplastic changes as well as an apocrine change and occasionally squamous metaplasia. Besides aggressive local infiltration, hematogenous metastasis of the skeletal system and lungs is common. Therapy is dependent on the extent of local tumour growth as well as on the degree of metastasis and usually takes the form of radical mastectomy with lymphadenectomy and postoperative radiotherapy. Local recurrence is found in over 50% of the cases and the 5-year survival rate is in the order of 70%.