Ultrastructure of cystosarcoma phyllodes and fibroadenoma. A comparative study.

Electron microscopic studies were conducted on 11 cases of cystosarcoma phyllodes (6 benign, 3 malignant, 2 recurrent), 1 stromal sarcoma, and 15 cases of fibroadenomas. Particular emphasis was placed on examination of the epithelial-stromal junction. The epithelial cells were basically similar in all cases. The basal lamina of fibroadenomas tended to be reduplicated, whereas in cystosarcoma phyllodes the basal lamina was less reduplicated and even focally absent. A continuous layer of delimiting fibroblasts was not present in either type of tumor. Stromal cells were generally fibroblasts, with 2 of 15 being fibroadenomas and 2 of 11 cystosarcoma phyllodes showing myofibroblastic differentiation. The stromal sarcoma also showed smooth muscle differentiation. The authors conclude that the epithelial-stromal junction is abnormal in both fibroadenomas and cystosarcomas, but the abnormality is different in these two tumors. Increasing prominence of stromal cell junctions and of lysosomes also correlated with the diagnosis of cystosarcoma, particularly the malignant variant.