Metabolism of steroids by human brain tumors.

Hormonal steroids or their precursors can be metabolized in the CNS to products with altered hormonal activity. The importance of the intracerebral transformation of steroids has been demonstrated, particularly with regard to neuroendocrine regulation and sexual behavior. These studies were carried out on normal brain tissues, but the ability of neoplastic tissues of CNS origin to metabolize steroids is unknown. We investigated the in vitro metabolism of tritiated pregnenolone, testosterone, and estradiol-17 beta by homogenates of four brain tumors defined as astrocytomas. In three tumors of cortical origin, removed from adult patients, the only enzymic activity found was the conversion of estradiol to estrone. In one tumor of cerebellar origin removed from an 11-year-old boy, the following conversions were found: pregnenolone to progesterone, testosterone to either androstenedione or estradiol, and estradiol to estrone. These results demonstrate that human astrocytomas can transform steroids to compounds with modified hormonal activity. These compounds formed by the tumorous tissue can affect brain function, which may be of clinical significance. Furthermore, these results may add important parameters for biochemical characterization of neoplastic brain tissues.