An immunohistochemical and ultrastructural investigation on the presence of "smooth muscle differentiation" in stromal ovarian tissue was carried out in 10 adult granulosa cell tumors, six juvenile granulosa cell tumors, six thecoma/fibrothecomas, six cases of stromal hyperplasia, and in 10 normal ovaries. For immunohistochemistry, formalin-fixed paraffin-embedded tissues were processed using anti-alpha smooth muscle actin (alpha-SM actin) and anti-desmin as primary monoclonal antibodies. All adult granulosa cell tumors and juvenile granulosa cell tumors showed an intense alpha-SM actin immunoreaction, but weaker for desmin. Immunostain was diffuse in six out of 10 and five out of six adult granulosa cell tumors and juvenile granulosa cell tumors, respectively. Ultrastructurally, intermediate filaments focally converging into well developed desmosomes as well as peripheral bundles of myofilaments were documented both in adult granulosa cell tumors and juvenile granulosa cell tumors. In thecoma/fibrothecomas and stromal hyperplasia, alpha-SM actin and desmin expression was minimal or absent; on electron microscopy some "myoid" features and myofibroblasts were also seen. In normal ovaries, alpha-SM actin was found intensely expressed in the theca externa, focally identified in cortex-medulla, and unstained in the theca interna layer. Immunoreaction increased during folliculogenesis, going from a thin positive alpha-SM actin layer around secondary follicles to a strong diffuse stain in mature follicles. Our immunohistochemical and ultrastructural results indicate that a "smooth muscle differentiation" is a typical component of the specialized gonadal stromal tissue. A diffuse and focally alpha-SM actin is constantly present in granulosa cell tumors and thecoma/fibrothecomas, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
Actins Adult