Mechanisms responsible for oestrogen receptor expression in primary human breast cancer

Oestrogen receptor (ER) status in human breast cancer provides the best parameter available at present to determine the likely response to endocrine therapy. However, the precise mechanisms responsible for ER expression have yet to be fully elucidated. In order to examine this we have quantitatively analysed the mRNA and protein levels of ER in 61 patients with primary breast cancer using the techniques of ribonucleic acid (RNA) slot blotting and immunocytochemistry. Using the H222 monoclonal antibody, ER staining was observed in 40 cases (65.5%) following immunocytochemical assay. RNA slot blotting using a complimentary deoxyribonucleic acid probe (HEO) revealed ERmRNA to be present in 46 cases (75.4%). The mRNA and protein levels of ER were found to be significantly correlated (rs = 0.753, P < 0.0001). Exclusion of 15 cases where neither mRNA nor protein was detected still revealed a significant correlation in the remaining 46 cases (rs = 0.529, P = 0.0002). In 39 cases sufficient RNA was obtained to allow further filters to be prepared containing larger amounts of RNA. The results obtained in these filters showed high concordance with those obtained originally for these patients (rs = 0.915, P < 0.0001), validating the results. Our results suggest that ER expression in primary breast cancer is determined either by transcriptional modulation or by increased transcript stability.