A new approach allowing an early prognosis in breast cancer: the ratio of estrogen receptor (ER) ligand binding activity to the ER-specific mRNA level.

We have performed a quantitative analysis of steady-state levels of ER-mRNA for 88 untreated, primary breast carcinomas. We compared the amount of specific mRNA with the amount of ER receptor measured, through ligand binding activity, by calculating the ratio R = [ER-protein/ER-mRNA]. This analysis showed that the relative level of ER-mRNA displayed a large range of values partly related to the concentration of ER-protein. We found a greater percentage of tumors with a high R ratio value in the tumor population containing elevated levels of ER-protein. A statistical analysis performed on a homogeneous population of 63 patients shows no correlation between the R ratio, lymph-node involvement and histological grade. However, R appears to be significantly related to the risk of relapse within a relatively short period of time following the first observation. An R value higher than 1.5 appears to constitute a significant and early prognostic factor of recurrence (P = 0.003).