Oestrogen receptor assay--limitation of the method

Estrogen Receptor analyses in the Danish Breast Cancer Cooperative Group. History, methods, prognosis and clinical implications

INTRODUCTION

Estrogen receptor (ER) is a prognostic and predictive biomarker, which has been known for 40 years. The detection method has developed over the years from different biochemical assays (BCA) to immunohistochemistry (IHC) on paraffin embedded tissue. The aim of the present study is to describe the development in ER analysis in the Danish Breast Cancer cooperative Group (DBCG), in the period of 1977 to 2006, regarding quantity and method of analyses. To compare BCA with IHC, and to report the prognosis for low-risk breast cancer patients.

PATIENTS AND METHODS

In the period of 1991-1993, BCA and IHC were both performed on 2 364 tumours from breast cancer patients in Denmark. Three central laboratories in Copenhagen, Aarhus and Aalborg, respectively, performed BCA, while IHC was done in each of the pathology departments participating in the study. Data on ER status, clinical variables and prognostic factors were obtained from the DBCG database. Prognosis is calculated from the DBCG protocol 89a, regarding recurrence free survival (RFS) and overall survival (OS).

RESULTS

We find an increasing frequency of ER positive tumours over time, with correlation to patient age. There is a better RFS and OS for tumours positive in both ER determinations. However, BCA is more sensitive than IHC. We find a significant correlation between positive ER status and other low risk factors, except lymph node status.

DISCUSSION

Immunohistochemistry has several advantages compared with BCA; it is decentralised, only requiring small amounts of tumour tissue, with direct light microscopic interpretation of invasive tumour cells. It is less expensive and more rapid than BCA. Results in this study show the same RFS in both ER determinations. We conclude that IHC in analysing ER is a rapid, reliable and easy method, and we recommend the use of external quality control programme.

Estrogen receptor antibodies: specificity and utility in detection, localization and analyses of estrogen receptor alpha and beta

The role of estrogens in regulating cellular metabolism in many tissues is well documented. Estrogens regulate cellular activity by interacting with specific intracellular receptor proteins. Two estrogen receptor (ER) isoforms have been isolated, cloned and characterized. Estrogen receptor alpha (ERalpha) and beta (ERbeta) are ligand dependent transcriptional activators, which regulate gene expression via complex mechanisms requiring ligand binding, transformation, dimerization, and interaction with specific unique cis DNA hormone response elements (EREs) and co-activators and co-repressors. Studies of ER structure and function have been tremendously facilitated by the development of molecular and biologic probes. Cloning and functional studies of the ERalpha and ERbeta have delineated some of the structural requirements involved in receptor function. Immunochemical analyses together with biochemical and molecular approaches have contributed to our understanding of ER structure and function. Although antibodies to ER have been developed and utilized for the past two decades, there has yet to be a comprehensive review that discusses the utility and usefulness of these antibodies in receptor detection and analysis. In this review, we summarize a plethora of information concerning the development and characterization of site-directed monoclonal and polyclonal antibodies to the ERalpha and ERbeta. We provide critical discussion on the characteristics and utility of ER antibodies in analyses, characterization and localization of ER isoforms in various tissues. We also provide a comparison of the potential utility of the available antibodies in various immunochemical assays. An epitope map detailing the specific sites of antibody-receptor interactions is constructed based on the available information. The advent of antibodies with high specificity and titer had facilitated detection of ER isoforms in normal and neoplastic tissues. The advent of new antibodies remains a powerful tool for assessment of ER expression and post-translational modification and receptor function in many experimental systems.

The effect of 3-week tamoxifen treatment on oestrogen receptor levels in primary breast tumours: a flow cytometric study

The effect of 3-week, preoperative tamoxifen treatment on oestrogen receptor (ER) levels, expressed by primary breast tumours, was examined. Patients (age-matched) with breast cancer, confirmed by fine-needle aspiration, were either treated with 20 mg ml(-1) oral tamoxifen per day or received no medication in the 3-week interval between assessment and surgery. Quantification of ER using flow cytometry was performed on the surgically removed tumour samples from tamoxifen-treated (n = 40) and control (n = 38, untreated) patient groups. The tumours were mechanically disaggregated, and saponin treatment rendered these cells permeable to antibodies. Using dual-parameter labelling with a FITC-conjugated antibody (NCL-5D3) directed against cytokeratin 8/18/19 and a biotinylated antibody (DAKO-ER 1D5) directed against the oestrogen receptor, ER quantification was determined on a number of receptors per cell basis. Using QC quantum bead standards, ER levels in the epithelial cell population, the non-epithelial cell population and the whole-cell population (ER+) were calculated. ER levels were significantly lower in the total cell population than tamoxifen-treated patients (P = 0.002) when compared with the control (untreated) group. By using a gating procedure using 5D3 antibody positivity, a significantly lower level was detected on examining the cytokeratin-positive population alone (P = 0.006). Using a complementary gating technique, ER levels were quantified in the cytokeratin-negative cell population. Examination of this group of cells showed no significant difference between the levels of oestrogen receptor found in the tamoxifen-treated and untreated groups (P = 0.4). We have demonstrated that ER levels can be monitored by flow cytometry. ER levels in patients treated with tamoxifen 3 weeks before operation are significantly lower than in a comparative group of patients who received no drug. Furthermore, the most significant difference in receptor levels is seen by quantification of total ER levels expressed by all the tissue.

Use of the biotinylated antibody DAKO-ER 1D5 to measure oestrogen receptor on cytokeratin positive cells obtained from primary breast cancer cells

A method for the use of a biotinylated antibody (DAKO-ER 1D5) to quantify oestrogen receptors (ER) on tumour cells by flow cytometry is described. ER quantification was determined after treatment with saponin rendering cells permeable to ER antibody. Use of dual parameter labelling was performed utilizing a FITC-conjugated antibody (NCL-5D3) directed against cytokeratin 8/18. This allowed selection of breast cancer cells of epithelial origin by gating to exclude contaminating inflammatory and stromal cells. Use of such a gating technique was seen to identify cells with a higher level of ER expression. Using QC quantum bead standards, the number of ER binding sites per cell was assessed. Results were compared with conventional ER quantification using a radio-ligand binding assay. A high degree of correlation was found between the two methods. The flow cytometric method for ER quantification described is simple, rapid, and reproducible. The assay may be of particular value in measuring ER on urgent clinical samples. Advantages of this assay over the radio-ligand binding assay include reduction in use of radio-labelled iodine compounds, a decrease in analysis time, and reduced cost and quantity of material needed for assay.

Expression of transforming growth factor beta (TGF beta) receptors and expression of TGF beta 1, TGF beta 2 and TGF beta 3 in human small cell lung cancer cell lines

A panel of 21 small cell lung cancer cell (SCLC) lines were examined for the presence of Transforming growth factor beta receptors (TGF beta-r) and the expression of TGF beta mRNAs. By the radioreceptor assay we found high affinity receptors to be expressed in six cell lines. scatchard analysis of the binding data demonstrated that the cells bound between 4.5 and 27.5 fmol mg-1 protein with a KD ranging from 16 to 40 pM. TGF beta 1 binding to the receptors was confirmed by cross-linking TGF beta 1 to the TGF beta-r. Three classes of TGF beta-r were demonstrated, type I and type II receptors with M(r) = 65,000 and 90,000 and the betaglycan (type III) with M(r) = 280,000. Northern blotting showed expression of TGF beta 1 mRNA in ten, TGF beta 2 mRNA in two and TGF beta 3 mRNA in seven cell lines. Our results provide, for the first time, evidence that a large proportion of a broad panel of SCLC cell lines express TGF beta-receptors and also produce TGF beta mRNAs.

Enzyme immunoassay of oestrogen receptors in needle biopsies from human liver

For quantitative assessments of sex hormone receptors in liver tissue, ligand binding assays are inconvenient, as they require large biopsies (0.5-1.0 g). The present study shows that it is possible to measure oestrogen receptors (ER) quantitatively in needle biopsy specimens as small as 10 mg by modifications of a commercial enzyme immunoassay employing monoclonal antibodies. Sucrose gradient centrifugation and the dextran charcoal method served as reference methods. A consecutive series of needle biopsies from patients suspected of liver disease were investigated. The biopsies (n = 37) had a median weight of 14 mg and cytosolic protein concentrations greater than 1 mg/ml (median 1.28 mg/ml). The median ER concentration was 20 fmol/mg cytosolic protein (range 5 to 57 fmol/mg). The intra-assay coefficient of variation was 8.9%, the inter-assay 13.2%, and the detection limit 2.7 fmol/ml cytosol. Women had significantly higher ER concentrations (median 22 fmol/mg) compared to male patients (median 16 fmol/mg) (P = 0.007). The enzyme immunoassay measures ER in liver specimens as small as 10 mg, compared to the large tissue specimens necessary for the conventional DCC assay, and the method is a convenient tool for further studies of ER in routine needle biopsies from the liver.

Characterization of estrogen receptor in human gastric cancer

Estrogen receptors (ER) were examined in cytosol, nuclear potassium chloride (KCl) extractable fraction, and nuclear KCl unextractable fraction by the dextran-coated charcoal adsorption method in various gastric cancer tissue. The overall ER-positive rate in the cytosol and nuclear fraction was 19.2%. The maximum binding site (Bmax) was 36.0 to 175.0 fmol/mg of protein, and the dissociation constant (Kd) was 0.6 to 1.6 X 10(-9) in cytosol fraction. In the nuclear fraction, Bmax was 7.5 fmol/mg of DNA and Kd was 2.3 X 10(-9). Estrogen receptors were characterized in cytosol protein. In cytosol, the estrogen (E2)-ER complex was sedimented at approximately the 5S and 8S regions by 5% to 20% linear sucrose gradient centrifugation. A steroid specificity study of ER showed the presence of an binder in gastric cancer tissue. In conclusion, these results that gastric cancer tissue has E2 binding sites with the same biochemical characteristics as in breast cancer and endometrial cancer strongly suggest the hormonal dependency of gastric cancer.

Demonstration of oestrogen and progesterone receptors in freeze-dried, paraffin-embedded sections of breast cancer

Immunohistochemical evaluation of oestrogen and progesterone receptors is of importance in evaluating human breast tumours. Staining techniques can be performed on snap-frozen, cryostat-cut tissues or, as recently reported, on formalin-fixed, paraffin-embedded tissues. These methods are, however, limited by several drawbacks, including difficulties in retrospective studies and in storage of the material, and the relatively high frequency of false negative results for chemically fixed specimens. We therefore investigated the application of freeze-drying technology to assess the feasibility and reliability of this technique as an alternative method for diagnostic breast pathology. Morphological and immunohistochemical studies were performed on snap-frozen, freeze-dried and paraffin-embedded tissue obtained from 16 cases of benign and malignant breast neoplasms. Our results showed good preservation of tissue morphology, similar to standard formalin fixation, and excellent preservation of antigenic reactivity of nuclear receptors, comparable to that obtained with cryostat sections. We therefore suggest that freeze drying and paraffin embedding of frozen tissue blocks is equivalent or even preferable to formalin fixation for the demonstration of oestrogen and progesterone receptors, at least in the case of small tumours.

A comparative study of histopathology, hormone receptors, peanut lectin binding, Ki-67 immunostaining, and nucleolar organizer region-associated proteins in human breast cancer

The current study was performed on 71 cases of human female breast cancer and compares the results of five morphologic methods developed for the detection of estrogen receptors (ER), progesterone receptors (PgR), lectin Peanut agglutinin (PNA) binding sites, monoclonal antibody Ki-67 immunoreactivity, and the mean number of argyrophilic nucleolar organizer regions (Ag-NOR). All the parameters were evaluated on serial cryostat sections representative of a closely related, if not identical, neoplastic population. A significant positive correlation was found between the occurrence of estrogen, progesterone, and peanut receptors and between Ki-67 immunoreactivity, mean number of NOR, and mitotic index. Furthermore, ER, PgR, and PNA receptors showed a significant, inverse correlation with Ki-67 immunoreactivity, mitotic index, and mean number of Ag-NOR. These results provide further data that support the hypothesis that (1) progesterone and PNA receptors are estrogen-induced and indicate a metabolic response of the target cells to functioning estrogen receptors; (2) the mean number of NOR reflects the cell kinetics of the tumor; and (3) metabolic differentiation of neoplastic cells is inversely correlated to the proliferation index.

Demonstration of oestrogen receptor in symptomatic breast carcinoma, using fine needle aspiration cytology

Oestrogen receptor immunocytochemical assay (ER-ICA) was used to determine oestrogen receptor (ER) content of cells in fine needle aspirate (FNA) specimens from 88 breast carcinomas. In 49 of these the radioligand binding assay for oestradiol was available for comparison. The predictive value of ER-ICA staining for a positive radioligand binding assay (greater than 10 fmol/mg protein) was 95%. Although the predictive value of negative staining was only 66%, 34 out of 37 ER-ICA negative tumours had radioligand binding assays below 60 fmol/mg protein. ER-ICA staining showed a strong positive correlation with age of the patient, positivity being rare before the menopause. There was a weak inverse correlation with tumour grade but none with tumour size or lymph node status. The assessment of ER by immunocytochemistry using FNA cytology is a rapid technique, which may easily be repeated and provides a pre-operative assessment of ER status. It allows confirmation that tumour cells are present in the sample and an assessment of tumour heterogeneity.

What's new in steroid receptor immunocytochemistry in clinical oncology?

In this review we outline the many practical advantages of immunocytochemistry for estrogen receptors (ER) and the staining intensity index for its interpretation. We discuss the heterogenous distribution of ER in malignant and non-malignant breast tissue and the correlation of ER staining with pathologic features. In predicting the response of breast cancer to endocrine therapy, we conclude that both fine needle aspirates and tissue sections are adequate for the assessment of ER.

Image cytometry of estrogen receptors in breast carcinomas

A significant level of estrogen receptors (ER) in breast cancer cells is an indication of tumor differentiation and suggests that a homeostatic control of cell growth may persist in these cancers. In medical practice, the Dextran-coated charcoal assays (DCCA) are still the most frequently used test to characterize patients having ER-positive malignant breast tumors and for whom hormonal therapy is justified. Nevertheless, this routine biochemical technique is not satisfactory because it is a broad method unsuitable for revealing receptor tissue heterogeneity. However, immunocytochemical labeling, such as the ER-ICA method, which involves a monoclonal antibody linked to peroxidase, is a specific reaction for this purpose but which until now was not quantitative. The present study uses an original cell preparation technique combining the PAP reaction with toluidine blue counterstain for image analysis on the SAMBA system. Special software has been developed for the quantitative analysis of immunocytochemistry in cancers. Results obtained showed a high correlation between the DCCA values and the score derived from the mean ER concentration per positive tumor cell and the labeling index. In addition, intracell and intratumor heterogeneity can be displayed according to several parameters and were shown to vary according to tumor and to antiestrogen (Tamoxifen) presurgical therapy.

In vitro response of cervical cancer cell lines CaSki, HeLa, and ME-180 to the antiestrogen tamoxifen

The effect of tamoxifen, a nonsteroidal antiestrogenic drug, on the in vitro growth of three cell lines derived from carcinoma of the uterine cervix (HeLa, CaSki, ME-180) was studied using the breast cancer cell line MCF-7 as a tamoxifen-sensitive control. Logarithmically growing cells were fed daily with medium containing 5% dextran-charcoal-treated fetal bovine serum (D5) and 0, 1, 2.5, 5, 7.5, or 10 microM tamoxifen. The cell number in replicate cultures was assessed every other day by cell counts. Growth inhibition was expressed as the percentage of the cell number in control cultures fed with D5. At a concentration of 5 microM tamoxifen, a clear decrease in cell proliferation, resulting in 66-74% inhibition of growth, was observed with MCF-7, HeLa, and ME-180 after 6 days of exposure to tamoxifen. Doses greater than 5 microM resulted in cytotoxicity and progressive cell loss. With the CaSki cell line, 2.5 microM tamoxifen induced more than 60% growth inhibition and 5 microM tamoxifen was cytotoxic. Tamoxifen-induced growth inhibition was reversed by removing tamoxifen from the cell cultures, and the cells resumed logarithmic growth after a lag period of 24-48 hr. MCF-7, but not the cervical carcinoma, lines required estradiol for complete and rapid recovery of logarithmic growth. Our results indicate that tamoxifen inhibits cell growth of these cervical carcinoma cell lines by a mechanism different from that in MCF-7.

Immunohistochemical analysis of estrogen receptors (ER) using formalin-fixed paraffin-embedded breast cancer tissue: correlation with clinical endocrine response

A new immunohistochemical assay utilizing anti-ER monoclonal antibodies (H 222, Abbott) for detection of ER in formalin-fixed paraffin-embedded breast cancer tissue has been clinically evaluated. It is shown that tumors containing immunoreactive epithelial cells are much better candidates for hormonal manipulation than those without. In addition, primary tumors and corresponding regional lymph node metastases contain qualitatively the same ER pattern. The potentials and limitations of the present method are discussed in relation to other well-known ER assays.

The Stockholm trial on adjuvant tamoxifen in early breast cancer. Correlation between estrogen receptor level and treatment effect

The paper presents interim results of an on-going randomized trial of adjuvant tamoxifen (40 mg daily for 2 years) versus no endocrine adjuvant therapy in postmenopausal women with early breast cancer. A total of 1407 patients were included in the study between November 1976 through June 1984. Estrogen receptor (ER) data were available on 1184 patients (84%). The median follow-up was 53 months. Adjuvant tamoxifen increased the recurrence-free interval (P less than 0.01) but had no significant effect on overall survival. Treatment failures were reduced by 25% (P less than 0.01) and deaths by 7% (P greater than 0.05). Tamoxifen mainly decreased the frequency of loco-regional recurrence whereas distant metastases were less affected. The treatment effect was independent of tumor stage but was significantly related to the estrogen receptor (ER) content of the primary tumor. Tamoxifen appeared ineffective among ER negative patients, and the greatest effect was seen among those with high levels of ER. The results indicate that the main mechanism of action of adjuvant tamoxifen is similar to that suggested in advanced disease, i.e. an interaction with the estrogen receptor.

Steroid receptors in breast cancer: sources of inter-laboratory variation in dextran-charcoal assays

The presently recognized correlations between various clinical parameters and the concentrations of estrogen and progesterone receptors in breast cancer biopsies are largely based on receptor values obtained using the dextran-coated charcoal (DCC) method. This assay method is highly sensitive to slight changes in assay protocol, and differences in assay methodology may account for the wide variation in proportions of receptor positive patients reported by different centers. A survey of various aspects of the assay method that may lead to reproducible, systematic differences in concentrations of receptor levels is presented; and methods of compensating for or correcting these potential differences are discussed. The following aspects are considered: a) constitution of biopsy tissue, b) method of tissue homogenization, c) absorption of ligands to surfaces, d) inclusion of molybdate in the assay buffer, e) composition of the DCC slurry, and f) handling of samples for liquid scintillation counting. Differences in methods used to homogenize tissue in Europe and the U.S.A. may account for differences observed in the correlation of DCC assay results obtained using the recently-introduced monoclonal ER-EIA technique.

Evaluation of a new oestrogen receptor assay

Replicate assays of oestrogen receptor (ER) concentration on 81 specimens of human breast carcinoma were performed to compare the ligand binding Sephadex separation method with a polystyrene bead linked anti-oestrogen receptor monoclonal antibody technique (enzyme immunoassay [EIA], Abbott Laboratories). Each specimen was homogenized and the cytosol divided into four fractions. Replicate assays by each method gave an estimate of reproducibility. The mean CV (coefficient of variation = standard deviation/mean) for the ligand binding method was 9.73% compared with a mean CV of 17.9% for the EIA method. In the clinically significant range of ER values, around the cut-off point between negative and positive assays, there was no difference in the precision of the two assays (Mann Whitney U-test). The correlation between methods gave a Pearson's Product Moment Correlation Coefficient (r value) of 0.822, significant at the P less than 0.001 level, indicating a close correlation between the two methods. The highest CVs for both methods were in the range of oestrogen receptor concentrations, below 10 fmol/mg cytosol protein. Using 10 fmol/mg cytosol protein as a cut-off between negative and positive assays, 9.87% of the specimens would be reclassified as either positive or negative by the new assay method. The new assay method is, therefore, acceptable for clinical use.

Progesterone receptor assays in low-protein cytosols: a modified charcoal-gelatin procedure

Quantitative measurement of steroid receptors including progesterone receptor (PgR) is usually accomplished by the dextran-coated charcoal (DCC) assay. At protein concentrations below about 1 mg/ml, however, serious underestimation of receptor content by DCC occurs, presumably because of adsorption of receptor to the charcoal and possibly to assay tubes, etc. We have therefore developed a modified charcoal-gelatin (MCG) procedure which largely avoids receptor losses even in samples with extremely low protein concentrations. In this MCG procedure, 0.1% gelatin is added to both sample and charcoal suspension, the charcoal content is increased to 1%, and dextran is no longer necessary. Comparison of the MCG procedure with the standard DCC and several other methods at decreasing protein concentrations shows that MCG retains acceptable efficiency for PgR at much lower protein than the others, even as low as 10 micrograms/ml. This MCG procedure will be useful in determining receptors for prognosis in very small human breast cancer biopsies, as shown here, but also for receptor determination in very small tissues such as specific brain regions, and for receptor assay during purification.

Characterization of the T61 human breast carcinoma established in nude mice

This paper gives a biological characterization of the T61 human breast carcinoma established in nude mice. The human origin of the tumour was verified by the demonstration of the presence of human chromosomes exclusively in the tumour cells. The tumour cells were found by chromosome analysis and flow cytometric DNA analysis to be aneuploid. By electron microscopy, the tumour cells were shown to display the characteristics of glandular epithelium; a light microscopic examination revealed morphological characteristics similar to those of an axillary metastasis of the patient from whom the T61 tumour was derived. Furthermore, the tumour was shown to contain classical receptors for oestrogen and progesterone. The growth of the tumour was characterized by gompertzian growth curves. Since the T61 tumour has a response pattern to endocrine treatment which differs from that described for other human breast tumours grown in nude mice, this tumour may provide a valuable supplement in the study of human breast cancer and endocrine treatment.

Immunocytochemical staining of estrogen receptor in paraffin sections of human breast cancer by use of monoclonal antibody: comparison with that in frozen sections

Estrogen receptor (ER) in human breast cancer tissues was demonstrated in paraffin sections as well as in frozen sections by immunoperoxidase methods using monoclonal antibody (H222) against ER. The avidin-biotin-peroxidase complex method was used for the paraffin sections fixed in cold buffered formalin, and the peroxidase-antiperoxidase method was used for the fixed frozen sections. The results were compared with the ER content in the respective tumor tissue determined by dextran-coated charcoal assay. The specific staining for ER was located exclusively in the nuclei of cancer cells in both paraffin and frozen sections. Differences in the intensity and distribution of nuclear staining within a section were often observed, suggesting heterogeneity of the ER content of individual breast cancer cells. In 24 breast cancer tissues studied simultaneously by both paraffin and frozen section methods, 21 (88%) showed similar evaluation of the presence of ER. The results of immunocytochemical staining agreed with those of the dextran-coated charcoal assay in 89 (82%) of the 109 paraffin-sectioned tumor tissues and in 24 (86%) of the 28 frozen-sectioned tissues, indicating that ER can be demonstrated immunocytochemically by use of paraffin as well as frozen sections.

An analysis of the decrease in the assayed level of charged bovine estrogen receptor observed at physiological ionic strength

Lower assayed levels of heifer uterine estrogen receptor (ER) occur at physiologic ionic strength when ER is separated from [3H]estradiol by Dextran-coated charcoal treatments, or by gel filtration on Sephadex or polyacrylamide resins. The assayed level of charged ER in buffers containing 150-200 mM ionic strength is approximately one-half that of ER levels assayed in buffers either at 0-50 or 400-450 mM ionic strength. Treatment of ER with trypsin or molybdate eliminates this observed reduction. Evidence is presented that the decrease results from a preferential adsorption of ER to the assay resins at 150-200 mM ionic strength. This adsorption is likely to be mediated by a hydrophobic region of the ER, which is removed by trypsin cleavage.

Pitfalls in the Dextran-coated charcoal assay of estrogen receptors in breast cancer tissue

This study investigated the influence of the degree of concentration of breast tumor cytosols on the apparent estrogen receptor content as measured by the Dextran-charcoal assay. It was found that the dilution of cytosols to 1-2 mg protein/ml frequently but not always causes highly underestimated receptor concentrations. This could not be explained by the protein loss through adsorption to the charcoal. The effect was also studied in the presence of gelatin, sodium molybdate or with limited trypsinization of the incubation mixture. Addition of 1 mg/ml gelatin in the Dextran-charcoal suspension was very useful in most cases in preventing dilution induced losses in receptor sites. Both trypsinization and addition of sodium molybdate produced increases in receptor concentrations that were not as susceptible to inactivation through dilution of the cytosol. These data suggest that the observed high variability in the dilution induced receptor losses can be explained by receptor heterogeneity: some receptor form(s) are either readily absorbed to or "stripped" by the charcoal particles. As a conclusion we recommend that in order to optimize the estrogen receptor assay as regards both binding sites and affinities the cytosol concentrations should be maintained as high as possible and a protein expander be included in the Dextran-charcoal suspension. Though sodium molybdate frequently gives considerable increases in estrogen binding sites it occasionally has an opposite effect. For this reason we hesitate to recommend its use in routine assays of estrogen receptors.

Oestrogen receptor assay. False positive analysis?

The influence of unlabelled oestradiol, DES, testosterone and R-5020/org 2058 on tritiated oestradiol binding was investigated in 162 ER positive cases of patients with primary breast carcinoma. A dextran-coated charcoal as well as a sucrose gradient method was applied. In 122 cases only unlabelled oestradiol and DES significantly displaced the binding of labelled oestradiol. In the remaining 40 cases, oestradiol, DES, as well as testosterone and R-5020/org 2058 were able to displace the high-affinity, saturable binding of tritiated oestradiol equally. Possible explanations of this new discovery are discussed.

Analysis and properties of the cytosolic estrogen receptor from rat thymus

The equilibrium association constant, KA, and the number of receptor binding sites, Bmax, that characterize the estrogen receptor present in rat thymus were determined using five different methods of data analysis on binding data obtained using a dextran-coated-charcoal assay. The methods of data analysis consisted of fitting the binding data directly to the hyperbolic binding function, fitting the data to the Lineweaver-Burk, Scatchard, and Woolf transforms of the hyperbolic function, and the direct linear plot method of Eisenthal--Cornish-Bowden. The Woolf and Eisenthal--Cornish-Bowden methods gave identical results indicating that added estradiol caused a decrease in KA (competitive inhibition) and a marked decrease in Bmax (noncompetitive inhibition). The Scatchard analyses gave only a very qualitative indication of this trend, while the Lineweaver-Burk analyses gave no indication of any such systematic trend. The results from the computationally more difficult fits to the hyperbolic binding equation were in agreement with the Woolf and Eisenthal--Cornish-Bowden results. Thus, the cytosolic thymus estrogen receptor from the rat shows both competitive and noncompetitive inhibition in the presence of endogenous or exogenous estradiol.

Ploidy level of human breast carcinoma. Relation to histopathologic features and hormone receptor content

The ploidy level was investigated by flow cytometric analysis in 143 cases of invasive intraductal mammary carcinoma. Aneuploidy was found in 70% of the tumours. Comparison of ploidy level with histopathologic features, hormone receptor status and clinical characteristics indicated that aneuploid tumours were mostly poorly differentiated (grade III) and oestrogen receptor negative (p less than 0.05). However, this applied only to postmenopausal patients. No correlation appeared between the progesterone receptor status and the ploidy level, but this parameter tended to predict the frequency of lymph node metastases. The possible prognostic significance of these findings is discussed.

Tumour epithelial cellularity and quantitative oestrogen receptor values in primary breast cancer

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Oestrogen receptors in human breast cancer. Problems of correlation with histopathological features

Histopathological factors which might explain inconsistency in published data attempting to correlate oestrogen receptor content (ER) and pathological features in primary breast tumours have been investigated in 194 cases. It was found, that unequal assessment of tumour type and of histological grading between observers is one important factor. In terms of grading, however, heterogeneity of growth pattern within the same tumour seems to be of greater significance. No significant correlation was found between histological type of tumour and ER content. However, a trend towards a correlation between the extent of tubule formation (as an indication of differentiation) and ER content was observed.

Human breast cancer: heterogeneity of estrogen binding sites

A patient who had two primary tumors in the same breast is described. Both tumors were infiltrating duct carcinomas, but they differed as far as histologic malignancy and estrogen-receptor-positivity are concerned. One tumor was estrogen-receptor-positive the other was estrogen-receptor-negative. The case illustrates the multicentric origin of breast cancer as well as its cellular heterogeneity. Problems of treatment are discussed.

Glucose-6-phosphate dehydrogenase activity in human breast cancer. Lack of association with oestrogen receptor content

The correlation between glucose-6-phosphate dehydrogenase activity and different tumour characteristics was investigated in human breast cancer tissue. The enzyme activity was measured by a histochemical method and the oestrogen receptor content by a dextran-coated charcoal assay. The proliferative activity of the tumours correlated positively with the glucose-6-phosphate dehydrogenase activity. No correlation was found between enzyme activity and tumour type and menopausal status, age, TNM-class nor oestrogen receptor content. Based on this investigation it is concluded that the activity of glucose-6-phosphate dehydrogenase reflects the proliferative status of the tumour but not the hormone dependency of the tumour.