Determination of oestrogen receptors by enzyme immunoassay

Molecular forms of the estrogen receptor in breast cancer

Estrogen receptors (ERs) of which two isoforms have been identified (alpha and beta) are subjected to phosphorylation, glycozylation, ubiquitination and other post-transcriptional conformational changes giving rise to a very high molecular heterogeneity. Partial proteolysis of these receptors, as well as their high tendency to associate within oligomeric structures, reinforces this property. Investigations demonstrated that this heterogeneity is not a biochemical artefact suggesting some biological relevance. Our purpose was to review this topic, especially with regard to ERalpha from breast cancers.

Comparison of enzyme immunoassay and immunohistochemical measurements of estrogen and progesterone receptors in breast cancer patients

Before replacing enzyme immunoassay of estrogen and progesterone receptors by immunohistochemistry, results of both methods were compared on 437 samples obtained from breast cancer patients (342 primary breast carcinomas, 16 local recurrences, 49 biopsies, and 30 tumor specimens obtained after neoadjuvant treatment). Immunohistochemistry (IHC) results were first assessed semiquantitatively on the basis of the estimated proportion of positive tumor cells, and then quantitatively using the "quick score." Semiquantitative IHC hormone receptors results (positive > or = 10%) correlated well with enzyme immunoassay status (positive >15 fmol/mg protein) in 358 surgical samples (342 primary tumors and 16 recurrences), with overall concordance rates of 89.9% and 82.1%, respectively. Among the 100 discordant cases, a large intraductal carcinoma component was observed in 7 of 36 cases for estrogen receptor (ER) and 15 of 64 for progesterone receptor (PR). Thirty-five discordant cases also were observed near the cut-off values. Hormone receptor levels by enzyme immunoassay correlated strongly with the quantitative IHC "quick score." Whatever the method, hormone receptor status was associated with histologic grade (SBR) and tumor size, whereas age correlated strongly with ER positivity. Similar results were obtained for biopsy specimens and posttreatment samples. This comparison improved the reliability of the IHC technique, which is currently routinely used for ER and PR determination in the authors' institution.

Evidence of an estrogen receptor form devoid of estrogen binding ability in MCF-7 cells

In MCF-7 breast cancer cells, hydroxytamoxifen (OH-Tam) up-regulates the estrogen receptor (ER) in a form unable to bind [(3)H]estradiol (E(2)). We show here that this property is not restricted to this antiestrogen. [(3)H]E(2) binding assays (whole cell assays, DCC assays on cell extracts) and enzyme immunoassays (Abbott) performed in parallel, establish the permanent presence of such unusual ERs in the absence of any exposure of the cells to a ligand. E(2) and the pure antiestrogen RU 58 668, which down-regulate ER, also decrease [(3)H]E(2) binding. In control cells, these ERs represent about the half of the whole receptor population; they also display a tendency to stabilize within the cell nucleus. Loss of E(2) binding ability appears irreversible, since we failed to label receptor accumulated under OH-Tam with [(3)H]E(2) or [(3)H]tamoxifen aziridine (TAZ). Cycloheximide (CHX), which blocks E(2)-induced down regulation of ER, failed to stabilize [(3)H]E(2) binding (whole cell assay) after an [(3)H]E(2) pulse (1 h), confirming that regulation of E(2) binding and peptide level are related to different regulatory mechanisms. Loss of binding ability could not be ascribed to any ER cleavage as demonstrated by Western blotting with a panel of ER antibodies raised against its various domains (67 kDa ER solely detected). We propose that loss of E(2) binding ability is related to the aging process of the receptor, i.e. it is progressively converted to a form devoted to degradation after it has accomplished its physiological role. Ligands may favor (E(2), RU 58 668) or impede (OH-Tam) this elimination process.

Improvement of quality control for steroid receptor measurements: analysis of distributions in more than 40000 primary breast cancers. French Study Group on Tissue and Molecular Biopathology

All French laboratories that routinely assay estradiol (ER) and progesterone (PR) receptors participate in the European EORTC quality control program based on twice-yearly analysis of 5 cytosolic preparations. This system has considerably reduced inter-laboratory variations, but does not cover all aspects of these assays. Analysis of receptor value distributions is also crucial to ensure that receptor measurements remain stable with time, independently of the laboratory and assay method. This study involved 83907 receptor assays carried out in the last 17 years by 17 laboratories belonging to the French Study Group on Tissue and Molecular Biopathology. The assays were based on radioligand binding (RLA) or immunoenzymology (EIA). For each laboratory, the medians and positivity rates were analysed according to two totally objective criteria, the patient's age and the year of assay, and according to histological grade and histological type of the tumor in order to verify the correlations classically described. Age-related distributions varied little between laboratories, compared with data published by 7 European EORTC laboratories [1]. The results remained relatively stable with time in the RLA method for ER and PR, and in the EIA method for PR. Median ER-EIA data showed a marked increase between 1987 and 1989, mainly due to changes in the quality of Abbott reagents during this period. Otherwise, this analysis confirms previous pathophysiological observations.

Steroid receptor distribution in 47,892 breast cancers. A collaborative study of 7 European laboratories. The EORTC Receptor Study Group

Seven laboratories of the EORTC Receptor Study Group reported the distribution of oestrogen (ER) and progesterone receptors (PR) routinely assayed in breast cancer cytosols. A low interlaboratory variability was demonstrated for the median values, and for the frequency of positive tumours as measured by enzyme immunoassay (EIA). Larger variations were found for the frequency of positive tumours, as measured by radioligand binding assay (RLA). They are probably due to differences in the cut-off levels and in the sensitivity of the assay. Analysis of the variability over time clearly demonstrated that the ER-EIA values initially increased compared with RLA. A possible source of variations could be the calibration drift in the ER-EIA kit. In conclusion, quality assessment of steroid receptors should be monitored by comparison of both common standards and distributions routinely obtained in each laboratory. In-house analysis over time is also essential for reagent survey.