DEMONSTRATION OF AROMATASE-ACTIVITY AND ITS REGULATION IN BREAST-TUMOR AND BENIGN BREAST FIBROBLASTS

Breast tumors from post-menopausal women contain higher amounts of est radiol than would be predicted from levels circulating in plasma. This observation raised the hypothesis that tumors may synthesize estradio l in situ and increase their tissue estradiol levels via this mechanis m, The key enzyme involved in tissue estrogen synthesis, aromatase, is present in breast tumors but, according to some investigators, not in sufficient concentration to be biologically meaningful. We postulated that foci of cells in breast tumors might contain high amounts of aro matase and this locally produced estrogen might act in a paracrine or autocrine fashion. To test this hypothesis, we utilized immunohistoche mistry to localize the aromatase enzyme, an histological scoring syste m to quantitate it, and culture of isolated breast cells to demonstrat e its potential regulation. In 26 archival breast tumors, 16 (62%) con tained aromatase by radiometric assay. With the immunohistochemical me thod, we detected areas with staining in the stroma as well as tumor e pithelial cells. Staining ranged from the intensity approaching that s een in placenta to levels just distinguishable from background. We ado pted an histological scoring system (H-score) from that used to quanti tate progesterone receptor levels in tissue and used it to quantitate aromatase activity. A higher histologic score was found in stromal spi ndle cells (13) than in tumor epithelial cells (4.8). The biochemical aromatase results correlated with the H-score of stromal but not epith elial cells. To further study stromal cells from tumors, we isolated s tromal cells from breast tumors and the benign areas of breast distal to the tumor and grew them in culture. Addition of dexamethasone, phor bol esters, and cyclic AMP analogues stimulated aromatase enzyme and m essenger RNA levels substantially. Use of aromatase enzyme inhibitors such as letrozole blocked estrogen production but did not alter aromat ase message levels. Epithelial cells, whether nonmalignant or cancer d erived, exhibited no regulation by dexamethasone, phorbol esters, or c AMP analogues.