in vitro studies of steroid hormones in neurofibromatosis 1 tumors and schwann cells the most common nf1 feature is the benign neurofibroma which consists predominantly of schwann cells dermal neurofibromas usually arise during puberty and increase in number throughout adulthood plexiform neurofibromas associated with larger nerves are often congenital and can be life threatening malignant peripheral nerve sheath tumors mpnst in nf1 are believed to arise from plexiforms in 510 of patients there are reports of increased potential for malignant transformation of plexiform tumors and increase in dermal neurofibromas during pregnancy these observations suggest that steroid hormones influence neurofibroma growth and our work is the first to examine steroid hormone receptor expression and ligandmediated cell growth and survival in normal human schwann cells and neurofibromaderived schwann cell cultures immunohistochemistry and realtime pcr showed that estrogen receptors ers progesterone receptor pr and androgen receptor are differentially expressed in primary neurofibromas and in nf1 tumorderived schwann cell cultures compared to normal schwann cells however there is substantial heterogeneity with no clear divisions based on tumor type or gender the in vitro effects of steroid hormone receptor ligands on proliferation and apoptosis of early passage nf1 tumorderived schwann cell cultures were compared to normal schwann cell cultures some statistically significant changes in proliferation and apoptosis were found also showing heterogeneity across groups and ligands overall the changes are consistent with increased cell accumulation our data suggest that steroid hormones can directly influence neurofibroma initiation or progression by acting through their cognate receptor but that these effects may only apply to a subset of tumors in either gender