Oestrogen receptor expression in normal breast epithelium

Higher levels of oestrogen receptor (ER) expression in normal breast epithe lium may compound the increase in breast cancer risk seen with prolonged es trogen exposure. In prior studies, we have used immunohistochemical ER assa ys on fresh frozen samples of benign breast tissue. Future studies will be more feasible on paraffin-embedded samples, and newer, more sensitive antib odies are now available. We examined 30 samples of paraffin-embedded breast epithelium from postmenopausal women with two antibodies, 6F11 and TE111. We find that the median Iabelling indices for ER are significantly higher u sing these antibodies, compared with previous results. The threshold for ER positivity will, therefore, have to be reset in future studies, since ther e are still many issues that remain to be resolved in this area. (C) 2000 E lsevier Science Ltd. All rights reserved.