Fine structure of cystosarcoma phyllodes with reference to smooth muscle tumors.

The fine structure of the stomal component of cystosarcoma phyllodes was compared with that of intracanalicular fibroademona, leiomyoma and leiomyosarcoma. The stromal cells of fibroadenoma was intermediate between fibroblasts and smooth muscle cells and may be designated as myofibroblasts. The stromal cells of cystosarcoma phyllodes have fulfilled the ultrastructural criteria for smooth muscle cells. Therefore, cystosarcoma phyllodes should be regarded as smooth muscle tumors or those of myoepithelial origin.