Lipoleiomyoma of the uterus: Immunohistochemical analysis of 11 cases.

Abstract

The histogenesis of uterine lipoleiomyomas (UL), which are commonly considered to be rare tumors, has not been fully clarified. The purpose of this study is to ascertain the actual incidence of UL, and to establish the origin of the lipomatous component in UL. Out of the total of 812 uterine smooth muscle neoplasms diagnosed over the period between May 2001 and May 2002, 11 were UL (1.4%). The tissue samples from all cases were routinely processed, and the lipid content was histochemically demonstrated with Oilred-O. This method was performed in areas, which were macroscopically suspected to contain fatty tissue. Selected sections were immunostained. Ten leiomyomas and one smooth muscle neoplasm of uncertain malignant potential, with various amounts of the lipomatous component were identified. In three tumors the lipomatous component consisted of mature lipocytes. In eight tumors, the perivascularly localized focal areas of cells with pale abundant cytoplasm similar to smooth muscle cells or to fibrocytes containing cytoplasmatic lipid droplets were found. Immunohistochemically, the cells in the perivascular areas were positive for S-100 protein, desmin, vimentin, neuron specific enolase, alpha 1-antitrypsin, CD 34 and collagen IV and were negative for alpha-smooth muscle actin. Additionally, these cells and mature lipocytes were negative for estrogen and progesterone receptors. Our results suggest that UL are not rare neoplasms and that lipomatous differentiation in leiomyomas can be found more frequently than expected. Immunohistochemical results indicate that lipomatous cells, as well as smooth muscle cells, derive from multi-potential undifferentiated mesenchymal cells.