Immunocytochemical versus biochemical receptor determination in normal and tumorous tissues of the female reproductive tract and the breast

The development of highly specific and sensitive monoclonal antibodies directed against human estrogen (ER) and progesterone receptors (PR) provides a new approach in precise histochemical receptor location independent of hormone binding. Over the years receptor determination was the domain of the radioligand-binding assay, in which receptors are measured by tritiated ligand and unbound ligand is removed by the dextran-coated charcoal (DCC) procedure. Presented here are the results and experiences obtained by the classic DCC and the immunocytochemical method in the different normal and tumorous tissues of the female reproductive tract and the breast. The results of both methods were compared, and overall concordance of the results was found to vary considerably among the different types of tissue analyzed. Best agreement (86%) was found for PR determination in breast cancer, and the lowest rate of concordance for ER determination in fibrocystic disease of the breast. Special attention was directed toward the heterogeneity of receptor distribution in the specimens examined. In all tissues investigated, ER and PR were located in the nuclei of cells in both paraffin and frozen sections. Staining intensity varied among different cell types and from cell to cell for a single cell type, as well as in tumorous and normal tissues. In breast cancer, randomly scattered single cell receptor positivity was distinguished from focal/clonal positivity. Paraffin-embedded lymph node metastases showed significantly weaker staining as compared with their respective primary tumors. In the normal ovary, the corpus luteum and the stromal layer of the outer cortex were revealed as highly receptive elements for progestins, whereas ER was barely demonstrable in the normal ovary. Benign serous and mucinous ovarian tumors showed opposite ER and PR distribution among the stromal and epithelial components. Of special interest were the highly significant changes in ER and PR content in the stromal and glandular cells of the different layers of the normal endometrium throughout the menstrual cycle.     

Correlation of immunocytochemical and immunohistochemical determination of estrogen and progesterone receptors in breast cancer

OBJECTIVE: To evaluate prospectively the degree of correlation between immunocytochemical (ICC) and immunohistochemical (IHC) determination of estrogen (ER) and progesterone receptors (PR) in breast cancer. STUDY DESIGN: Fine needle aspiration cytology (FNAC) of 101 primary breast cancers were immunostained for ER and PR. They were compared with similar determinations in formalin-fixed paraffin sections of biopsies from the same patients. In cases of discrepancy, the histologic result was considered the gold standard. RESULTS: For ER a cytohistologic correlation of 94%, with a sensitivity of 96.1% and specificity of 86.9%, was found. For PR the cytohistologic correlation was 71.2%, with a sensitivity of 65.7% and specificity of 83.8%. CONCLUSION: ICC determination of hormone receptors in routinely fixed smears obtained by FNAC is a simple method that correlates adequately with the results of IHC determinations, especially for ER.     

Value of ER-D5 immunocytochemical determination in routine tissue sections of human breast cancer

ER-D5 is a recently identified protein related to estrogen receptors (ER). Generally ER measurement requires fresh frozen tissue and for ER-D5 assay ethanol (E) fixation of the specimen is recommended. We evaluated the possibility of immunocytochemical detection of ER-D5 in routine formalin-fixed (F) sections in 51 breast cancers comparing the results with those obtained in the same specimens using E as fixative. The results of ER-D5 assay were expressed by the staining index (SI) taking values greater than or equal to 5 as positive. In all tumors ER was also assayed by a biochemical method (DCCA). The sensitivity of ER-D5 detection in F was only 33.3%, while the specificity was 94.4%. A lower cut-off value of SI for F sections (greater than or equal to 2) increased the sensitivity to 66.6%, leaving the specificity unchanged. A strong correlation was found between the SI of ER-D5 in E and F (p less than 0.001). The SI of ER-D5 in F sections was also well correlated with ER concentrations (p less than 0.001). These results suggest that immunocytochemical determination of ER-D5 in routine sections may be useful in retrospective studies of hormone dependence in breast cancer.     

Immunocytochemistry on scrape cytology in breast cancer: will it unearth the weaker positives?

OBJECTIVE: To standardize the technique of immunocytochemical (ICC) assessment of estrogen (ER) and progesterone receptor (PR) status in breast cancer by scrape cytology and to compare the results with immunohistochemistry on paraffin blocks. STUDY DESIGN: ICC assessment for ER and PR was done on scrape smears from tissue samples in 200 cases of primary breast cancer. The results were compared to those obtained from immunohistochemical (IHC) evaluation of formalin-fixed paraffin same tissue samples. RESULTS: ER/PR positivity rates as well as staining scores were compared between the scrape smears and tissue sections. The concordance between cytology and histology was 84% for ER and 90% for PR. Both the positivity rates and the staining intensity scores were higher for cytochemistry than for histochemistry. CONCLUSION: The ICC method on scrape smears is a simple test with rapid turnaround time. The sample required is small, and antigen loss due to fixation and processing is minimal. This new method gives a higher yield of hormone receptor positivity and, when used in conjunction with the IHC method, may improve the pickup rate of ER-positive cases, thereby playing an important role in risk stratification and therapeutic decision making in patients with breast cancer.     

Assessment of hormone receptors in breast carcinoma by immunocytochemistry and image analysis. II. Estrogen receptors

Frozen sections of 30 invasive breast carcinomas were stained for estrogen receptors (ERs) and the tumor cell proliferative rate by an immunoalkaline phosphatase technique. The stained sections were evaluated for ER by the microTICAS image analysis system. Seventeen tumors were ER positive and 13 were ER negative by image analysis. There was 93% concordance between the ER results obtained by image analysis and those obtained by biochemical methods. One case that was ER negative by image analysis was weakly positive by biochemical assay; a second case was ER positive by image analysis but ER negative by biochemical assay. Twelve of the 17 ER-positive tumors were diffusely positive while 5 displayed considerable intratumoral heterogeneity, with tumor cells exhibiting a broad range of intensity of receptor expression. In most cases, the image analysis ER status coincided with the progesterone receptor (PR) status, but in a large minority of cases (41%) the ER status and the PR status differed. Tumors with a high growth fraction (greater than 30%), as measured by Ki-67 immunostaining, were uniformly ER negative. The results of this investigation suggest that immunohistochemical staining of frozen sections for ER aided by automated image analysis (1) reliably detects the receptor in breast carcinoma, (2) allows for the assessment of heterogeneity within tumors and (3) may be used as part of a panel of antibodies to markers of potential prognostic importance in a single small tissue sample.     

Cytologic diagnosis of estrogen and progesterone receptors in breast imprints

OBJECTIVE: To investigate estrogen receptor (ER) and progesterone receptor (PR) levels in imprint specimens obtained at breast surgery and to compare their correlation with that of standard methods. STUDY DESIGN: Imprint specimens for cytology were obtained from 101 mass-forming lesions in 66 patients, and specimens were frozen in liquid nitrogen for later assay. The imprint specimens were immunocytochemically (ICC) stained by monoclonal antibody to ER or PR; diaminobenzidine-stained cell nuclei in clusters were regarded as positive. Tissue specimens were assayed by the standard method of dextran-coated charcoal assay (DCC) and enzyme immunoassay. RESULTS: Forty-five primary breast cancer lesions, 2 contralateral breast cancer, 49 dissected nodes and 5 benign breast lesions were collected. The correlation between DCC and ICC was 81% (82/101) for ER and 74% (66/101) for PR. That between EIA and ICC was 88% (88/99) for ER and 80% (79/100) for PR, higher than that between DCC and ICC for ER and PR. CONCLUSION: ICC assessment of ER or PR on imprint cytology is a promising clinical test with an acceptable correlation.     

Stereologic correlates of steroid receptor concentration in invasive ductal breast cancer

The hypothesis was tested that morphometric parameters of tumor cell nuclei correlate with the steroid receptor concentration in mammary carcinoma. In 50 consecutive mastectomy specimens with a diagnosis of invasive ductal cancer in which estrogen receptor (ER) and progesterone receptor (PR) concentrations had been assayed quantitatively, morphometric measurements were performed on four visual fields of two sections per case. The fields were sampled from the most cellular regions of the tumor. The number of tumor cell nuclear profiles per tissue area, the nuclear profile area and the long and short nuclear profile axes and their ratios were measured with a semiautomatic image analysis system. Estimates of the number of tumor cell nuclei per tissue volume (Nv) and of the mean tumor cell nuclear volume (V) were obtained by standard stereologic techniques. Association between the morphometric and biochemical parameters was tested by Spearman's rank correlation coefficient. Nv correlated positively with the steroid receptor concentration whereas V correlated negatively with both ER and PR concentrations. A correlation of the receptor concentrations to the standard deviation of the nuclear area or the mean ratio of the nuclear axes could not be demonstrated. These results suggest that receptor-rich tumors have a large number of small tumor cell nuclei whereas receptor-poor tumors have a small number of large tumor cell nuclei per tissue volume in the actively proliferating, highly cellular regions. These differences are not accompanied by significant changes in nuclear size variability or nuclear shape.     

Progesterone receptor quantification with radiolabeled promegestone (R 5020) in frozen sections of endometrium and breast cancer tissue

A technique for the determination of the progesterone receptor content at sections was developed. Series of coverglass-mounted unfixed frozen sections were incubated with [3H]R5020 only, to determine total binding, or with excess unlabeled R5020, to determine non-specific binding. Ligand binding in the tissue sections was measured by liquid scintillation counting after repeated washing of the coverslips. Elution of ligand binding proteins into the incubation buffer was quantitated with the dextran-coated charcoal method. Specific ligand binding was related to the total tissue protein content which was determined on parallel, unmounted sections. Scatchard analysis showed specific saturable and high affinity (Kd = 0.01-2 nM) section-bound and soluble binding sites in cryostat sections of calf uterus, human endometrium and breast cancer samples. Ligand specificity was studied by competition of [3H]R5020 with a 100-fold excess of various steroid receptor ligands. The competition was excellent for R5020 and progesterone, negligible for estrogens and slight for androgens and corticosteroids. These binding characteristics provide evidence that with this assay progesterone receptors are determined. Exchange experiments showed that with this method total, free as well as occupied, progesterone receptors can be measured. A highly significant linear correlation, and agreement in PR status classification between assay on cytosol and sections was obtained for a series of 21 breast cancer samples. Finally, progesterone receptor analysis using cryostat sections results in the recovery of 2-3 times more PR from the same amount of tissue as compared to the use of cytosol. These results indicate that progesterone receptors can be reliably assayed with Scatchard analysis using cryostat sections, which requires less tissue than the cytosol assay. This method, which is simple and easy to perform could be of practical importance, particularly when only small tissue samples (which also have to be analyzed morphologically or histochemically) are available and when quantitative radiochemical progesterone receptor data are required for direct comparison with (immuno-) histochemical information.     

The effects of sequential treatment with ethynyloestradiol and medroxyprogesterone acetate on oestrogen and progestogen receptors in breast cancer

As part of a clinical study designed to modulate oestrogen and progestogen receptor (ER and PR) binding site concentrations prior to chemotherapy ER and PR levels have been estimated immediately before treatment, after ethynyloestradiol (EE, 10 micrograms/day, 1 week) and after medroxyprogesterone acetate (MPA, 500 mg/day i.m., 2 weeks) in tumour tissue from 14 women with advanced breast cancer. There was no consistent change after EE treatment. MPA tended to decrease ER and PR levels, though some increases were also seen. Responses (10 complete and 3 partial remissions) to sequential cyclical hormono-chemotherapy were not related to ER or PR levels prior to chemotherapy.     

Expression of oestrogen receptor-beta in invasive breast tumours

Steroid hormone receptors are used routinely to predict endocrine responsiveness in patients with breast cancer. Two oestrogen receptors (ERs): ER alpha and ER beta have been identified. Although ER alpha and ER beta genes share a large degree of homology, it is generally thought that their distribution and function are substantially different in many tissues. Both of them may be expressed in normal and neoplastic tissues of the breast. While much is known about ER alpha, the role of ER beta is still undefined, especially at the protein level. Recent development of reliable antibodies to ER beta has provided opportunity to test immunohistochemical reactions detecting ER beta in archival breast tumours. The aim of our study was to learn more about the cellular mechanisms underlying the relationship of ER beta and progesterone receptor (PR) in breast cancer tissues, discriminating between hormone-dependent and hormone-independent tumours. ER alpha and PR content of tumour tissues of 154 patients with breast cancer were tested by in situ indirect immunohistochemical method parallel with ligand binding biochemical assay. ER beta was detected in 8 ER alpha-/PR+ breast carcinomas by immunohistochemical method too. Steroid hormone receptor content was analysed comparing to the histologic type and grading of the tumours. CONCLUSIONS: A considerable part of breast carcinomas belongs to the ER+/PR+ and ER-/PR- groups. About 1-2% of the tumours is expected to be ER alpha-/ER beta+/PR+ type. In such cases ER alpha negative reaction together with PR positivity can signal the necessity of the immunohistochemical detection of ER beta in routine histopathological practice, presenting the precise steroid hormone receptor status for the most effective endocrine therapy of the patients.     

A new assay of estrogen receptor by thin-layer gel filtration.

Application of a thin-layer gel filtration (TLG) method using Sephadex G-200 superfine for the assay of estrogen receptor (ER) is described. The method is based on the effective separation of specific receptor protein from nonspecific binding proteins and free hormone by TLG and subsequent determination of the radioactivity bound to specific ER. By the aid of fluorescein-labeled human γ-globulin, the position of specific ER can be visualized. The assay excludes completely the undesired fluctuation depending on the concentration of coexisting proteins and permits reliable and rapid quantitation of specific ER. Association constant and concentration of specific ER can be determined with 100 mg of mammary tumor tissue. The method has the additional advantage of not requiring expensive equipment.     

Protection of steroid hormone receptors by protease inhibitors

Steroid hormone receptors are proteolyzed by different types of enzymes present in target tissues. Effective protease inhibitors protecting steroid hormone receptors in various target tissues were investigated. Progesterone receptor (PR) in hen oviduct and estrogen receptor (ER) in cow uterus were specifically protected by relatively low concentrations (0.5 mM) of leupeptin or antipain (inhibitors of serine and thiol proteases). It was indicated that two different types of enzymes which modify native glucocorticoid receptor (GR) are present in rat liver. One was inhibited by 1 mM leupeptin or 1 mM antipain, while the other was inhibited by 1 mM phosphoramidon (inhibitor of thermolysin like proteases) or 10 mM sodium molybdate. Native PR, ER, and GR were shown to have similar Stokes radii (44 Å).     

Comparison of Four Immunochemical Methods For the Measurement of Oestrogen Receptor Levels In Breast Cancer

Four methods of assessing oestrogen receptor (ER) status were compared in 33 patients with operable primary breast cancer. The methods used to assess the ER status were immunocytochemical assay (ER-ICA) of frozen sections, fine needle aspirates and imprint material and enzyme immunoassay (ER-EIA) of tumour tissue. A mean overall ER positivity of 45% (15 out of 33), 41% (13 out of 32) and 21% (six out of 29) was obtained by immunocytochemical (ER-ICA) staining of frozen sections, fine needle aspirates and tumour imprints, respectively, and a mean overall ER positivity of 42% (14 out of 33) was obtained by ER-EIA. The concordance of ER positivity in pairs of data obtained from different method combinations was found to range between 72 and 91%. However, statistically there was no significant difference between the four methods on the basis of the data obtained. Good comparability has been shown between the three tissue analyses and therefore the method of choice is technically not immediately apparent.     

Immunochemistry for oestrogen receptor,progesterone receptor and HER2 on cell blocks in primary breast carcinoma

K. Kumar S, N. Gupta, A. Rajwanshi, K. Joshi and G. Singh Immunochemistry for oestrogen receptor, progesterone receptor and HER2 on cell blocks in primary breast carcinoma Objective: Steroid receptors and human epidermal growth receptor 2 (HER2) have been used for predicting response to treatment in breast cancers. Fine needle aspiration cytology can provide highly cellular material and can be used for such analysis. The present study was undertaken to assess the reliability of oestrogen and progesterone receptor (ER, PR) status and HER2 as demonstrated by immunochemistry (IHC) on cell blocks from breast carcinoma cases, in comparison with histological sections. Methods: IHC for ER, PR and HER2 was performed on cell blocks and their corresponding tissue sections of 50 primary pre‐chemotherapy breast carcinomas. Positivity for ER and PR was scored according to the Allred scoring system. Strong membranous positivity in more than 30% of tumour cells was considered positive for HER2. The tumours were classified as luminal A, luminal B, HER2‐over‐expressing and triple negative on the basis of ER, PR and HER2 status and results on cell blocks compared with histological sections. Results: Correlation between immunostaining on cell blocks and the corresponding tumour tissues revealed a concordance rate for ER, PR and HER2 of 90% [Correlation coefficient (r) = 0.79], 94% (r = 0.86) and 90% (r = 0.76), respectively. Including five cases in which cell blocks were either ER or PR positive, 43/50 cases (86.0%) could be correctly classified on cell block immunostaining alone. The main reasons for seven discordant cases included technical errors (sampling error and staining error) and interpretational error in HER2 evaluation on cell blocks; the core biopsy was inadequate in one, and apparently false negative for HER2 in another. Conclusion: Cell blocks are useful in the assessment of hormone receptor status and HER2 by IHC, especially in cases of locally advanced breast cancer for planning neoadjuvant chemotherapy. It is highly recommended to have good quality cell blocks and quality control of their interpretation.     

Expression of sex steroid receptors and IGF-1 mRNA in breast tissue--effects of hormonal treatment

The mechanisms behind increased breast tissue proliferation and a possibly increased breast cancer risk in women using hormonal contraception (HC) and hormonal replacement therapy (HRT) are incompletely understood. We analyzed breast tissue from 20 premenopausal and seven postmenopausal women undergoing reduction mammoplasties for estrogen receptor (ER) and progesterone receptor (PR) content as well as mRNA levels for ER, PR and insulin-like growth factor-1 (IGF-1). The receptor values were correlated to IGF-1 mRNA concentrations and levels of steroid and peptide hormones and SHBG. In women using HC, we found significantly lower ER values (p=0.02) but non-significantly lower ER mRNA levels compared to those in naturally cycling women. PR and PR mRNA were no different. Women on HC displayed a higher breast tissue proliferation (p=0.05) expressed as Ki-67, MIB-1 positivity, which was correlated with IGF-1 mRNA (r_s=0.82, p=0.04). Since the concentration of sex steroid receptors in breast tissue is comparatively low and steroid receptors are down-regulated during hormonal treatment, mechanisms other than direct sex steroid receptor action are likely to be present. Our results suggest a role for IGF-1 in the proliferative response of breast tissue during exogenous hormonal treatment.     

Estrogen and progesterone receptor content in the pituitary gland and uterus of progesterone-primed and gonadotropin releasing hormone-treated anestrous ewes

The objective of this work was to investigate the effect of progesterone (P) and gonadotropin-releasing hormone (GnRH) treatment on estrogen receptor (ER) and P receptor (PR) concentrations in the pituitary gland and uterus of anestrous ewes. Ewes were either not treated (group C, n = 4); were treated with 0.33 g P-controlled internal drug release (P-CIDR) for 10 days (group P, n = 4), with GnRH, 6.7 ng i.v. injections every 2 h for 18 h followed by a 4 microg bolus administration of Receptal at 20 h (group GnRH, n = 4), or with a combination of the P and GnRH treatment (group P + GnRH, n = 3). Ewes were humanely killed either at the beginning of the experiment (group C), when the CIDR was removed (group P), or 24 h after the GnRH bolus treatment (groups GnRH and P + GnRH). Progesterone treatment increased serum P concentrations, indicating that the treatment was effective. All GnRH treated ewes had similar luteinizing hormone (LH) surges, which lasted 8 h. At slaughter, estradiol (E2) concentrations in the GnRH group were higher than in groups C, P, and P + GnRH. Treatment with GnRH increased more than 10-fold the content of ER and PR in the pituitary gland without altering steroid receptor concentrations in the uterus. When GnRH was combined with P the uterine receptor contents were higher than with P treatment alone. The treatment with P decreased ER and PR content in the uterus, but had no effect on the pituitary gland. The results show that regulation by P and GnRH of ER and PR content in anestrous ewes is tissue-specific.     

Histochemical localization of estrogen and progesterone receptors: evaluation of a method

A histochemical method for the detection of estrogen (ER) and progesterone (PR) receptors in human endometrium, using estrogen and progesterone derivatives linked to fluorochrome-labeled bovine serum albumin (E2-BSA-fluorescein isothiocyanate (FITC) and progesterone-BSA-tetramethylrhodamine isothiocyanate (TMRITC], has been evaluated. The fluorochrome-labeled steroids were bound to the cytoplasm--preferably in glandular epithelial cells but to a lesser extent also to stromal cells. The steroid specificity of the observed binding was studied by preincubating the sections with a series of unlabled steroids and nonsteroidal, hormonally active compounds (estradiol-17 beta, diethylstilbestrol, tamoxifen, 5 alpha-dihydrotestosterone and R 1881 for ER and ORG 2058, R 5020, dexamethasone, cortisol and 5 alpha-dihydrotestosterone for PR). The inhibition studies indicated that E2-BSA-FITC and progesterone-BSA-TMRITC bind to ER and PR in human endometrium with a reasonable degree of specificity. The method was reproducible and various procedural steps were tested, showing satisfactory technical stability. The method is applicable to small tissue samples, and is a valuable complement to quantitative biochemical receptor assays, as it localizes the receptors in tissue slices.     

Quantification of estrogen- and progesterone receptors from cryostat sectioned human tumor tissue: comparison of ligand binding and immunocytochemical assays

We have recently described an assay procedure to measure estrogen and progesterone receptors in extracts from frozen sections by a ligand binding assay. With this methodological approach it is now possible to perform comparative experiments not only to DCC/Scatchard analyses from different tissue blocks, but also to immunocytochemical determinations in identical tissue blocks: (1) When receptor quantities measured by the two biochemical methods were compared, a high correlation of estrogen receptor content was found between determinations in supernatants from frozen sections and DCC/Scatchard analyses. A slightly poorer correlation in the comparison of the ligand binding assays was obtained for the progesterone receptor. (2) The percentage of tumor cells stainable by immunocytochemistry for estrogen and progesterone receptors could hardly be correlated to the receptor concentrations (fmol/mg) measured quantitatively by the two ligand binding assays. (3) As the final result tumor specimen could be grouped into classes of receptor status according to the presence or absence of a nuclear stain in immunocytochemical assays or according to receptor concentrations above or below distinct threshold which were fixed at 20 fmol/mg for Scatchard analyses of both receptor species, 20 fmol/mg for estrogen- and 40 fmol/mg for progestin receptors for the assay with sections. In this diagnostical consideration the concordance of both biochemical methods to the immunocytochemical assessment was high for estrogen and less pronounced for progesterone receptors. (4) In some breast cancer specimen analyzed biochemically an unspecific progestin binding component could be detected superimposed on the progesterone receptor peak after isoelectric focusing.     

Effects of quinestrol on reproductive hormone expression, secretion, and receptor levels in female Mongolian gerbils (Meriones unguiculatus)

Quinestrol, a synthetic estrogen with marked estrogenic effects and prolonged activity, has potential as a contraceptive for Mongolian gerbils. The objective of this study was to describe the effects of quinestrol on reproductive hormone expression, secretion, and receptor levels in female Mongolian gerbils. Serum and pituitary concentrations of follicle stimulating hormone (FSH) and luteinizing hormone (LH) were decreased, whereas serum concentrations of estradiol (E2) and progesterone (P4) were increased after quinestrol treatment; the effects were both time- and dose-dependent. Furthermore, quinestrol downregulated expression of FSHβ and LHβ mRNA in the pituitary gland, as well as FSH receptor (FSHR) and estrogen receptor (ER) β in the ovary. However, it up-regulated mRNA expression levels of ERα and progesterone receptor (PR) in the pituitary gland and uterus, as well as mRNA for LH receptor (LHR) and PR in the ovary (these effects were time- and dose-dependent). In contrast, quinestrol had no significant effects on the mRNA expression levels of ERα in the ovary, or the gonadotropin α (GtHα) subunit in the pituitary gland. We inferred that quinestrol impaired synthesis and secretion of FSH and LH and that the predominant ER subtype in the pituitary gland of Mongolian gerbils may be ERα. Overall, quinestrol disrupted reproductive hormone receptor expression at the mRNA level in the pituitary-gonadal axis of the Mongolian gerbil.     

Flow cytometric analysis of estrogen, progesterone receptor expression and DNA content in formalin-fixed, paraffin-embedded human breast tumors.

Flow cytometric analysis of estrogen (ER) and progesterone (PgR) receptor expression in archival human breast tumors is relatively difficult. We have used enzyme digestion and microwave antigen retrieval procedures for multiparametric flow cytometric analysis of ER and PgR expression and DNA content in nuclei isolated from formalin-fixed/paraffin-embedded primary breast tumors. Deparaffinized rehydrated tissue sections treated with pepsin were subjected to microwave irradiation for unmasking of ER and PgR antigenic sites. Biotinylated ER antibody and streptavidin-fluorescein isothiocyanate (FITC) were used for ER labeling and PgR antibody with phycoerythrin labeled goat anti-mouse antibody was used for PgR labeling. Counter staining with propidium iodide-RNase was used for determination of cellular DNA content. Our results show that enzyme digestion and microwave treatment of formalin-fixed, paraffin-embedded breast tumors can be successfully used for the multiparametric analysis of nuclear hormone receptor expression and DNA content by flow cytometry.