Electron microscopy of uterine leimyosarcomas.

Electron microscopic studies of uterine leiomyosarcoma disclose a wide range of differentiation in the neoplastic cells. According to the cytoplasmic appearance undifferentiated, myoblastic, and fibroblast-like cells can be distinguished. Derivation of these cells from mesenchymal cells or poorly developed smooth muscle cells of the myometrium is suggested by the finding of numerous variously differentiated intermediate cell types. The cytoplasm of more differentiated tumour cells usually contains myofilament bundles. Three types of filaments are detected: small, intermediate and thick ones. While the thin ones probably are actin filaments, the intermediate and thick filaments are suggested to represent nonspecific filaments described in a variety of other cell types. Fibroblastic cell types are more often encountered and are usually better differentiated in the premenopausal woman. The possible role of endogenous hormonal factors on the differentiation process of tumour cells is discussed.