[Potential malignancy of cystosarcoma phyllodes of the breast. A contribution to the histogenesis of fibrosarcoma].

The present case report, which describes the transformation of a cystosarcoma phylloides into a "borderline case" and subsequently a fibrosarcoma, makes it clear that fibrosarcoma of the breast cannot always be regarded as a tumor which has developed primarily from mesenchymal breast tissue. Just as a benign cystosarcoma can turn malignant if therapy is inadequate, it can also turn into a purely sarcomatous tumor. The clinical consequences of this are that a cystosarcoma should not only be shelled out, but excised generously, with a wide border of healthy tissue. The "borderline" type of cystosarcoma phylloides, or respectively the fibrosarcoma, requires far more aggressive therapy, i.e., mastectomy. In fibrosarcoma cases additional selective lymphadenectomy may be considered, although the metastasization pattern is predominantly hematogenic. Overall, however, the prognosis for fibrosarcoma cases is better than for those with breast cancer.