Elastin in adenomatoid tumor. Light microscopic and electron microscopic study.

Elastin distribution was examined in adenomatoid tumors of the human genital tract. Two distinct patterns were identified: strongly positive or completely negative for elastin in the stroma, according to the case. Even in cases appearing to have very similar histologic features, the stroma was rich in elastin in some cases and was almost devoid of elastin in others. Electron microscopic examination with tannic acid staining revealed that the elastin in the stroma was composed mainly of amorphous material surrounded by a small amount of microfibrils and abundant collagen fibers. Fibroblasts were sparsely distributed in the stroma. Tumor cells displayed mesothelial cell-like features, such as abundant microvilli on the surface, numerous cytoplasmic organelles, several well-developed basal lamina. In some areas, elastin seemed to be formed by mesothelial cells. In some adenomatoid tumor cases, elastogenesis would be enhanced by activated mesothelial tumor cells as well as stromal fibroblasts.