Progesterone receptor determined by immunocytochemical and biochemical methods in human breast cancer

Breast cancer patients with progesterone receptor PR-A-rich tumors have poorer disease-free survival rates

PURPOSE

No study has yet analyzed whether changes in relative expression levels of progesterone receptor (PR) isoforms A and B in human breast tumors have significance in predicting clinical outcome. Human PRs are ligand-activated nuclear transcription factors that mediate progesterone action. Their presence in breast tumors is used to predict functional estrogen receptors (ERs) and, therefore, also to predict the likelihood of response to endocrine therapies and disease prognosis. The two PR isoforms, PR-A and PR-B, possess different in vitro and in vivo activities, suggesting that in tumors, the ratio of their expression may control hormone responsiveness. In general, PR-B are strong transcriptional activators, whereas PR-A can act as dominant repressors of PR-B and ER. Thus their balance may affect tamoxifen response in breast cancers.

EXPERIMENTAL DESIGN

To determine whether differential expression of the PR isoforms is associated with clinical outcome and hormonal responsiveness, PR-A and PR-B were measured by immunoblot analysis of cell lysates from 297 axillary node-positive breast tumors.

RESULTS

Expression of the two isoforms correlated with each other, as well as with ER. Additional analyses revealed that patients with PR-positive tumors but high PR-A:PR-B ratios, which were often caused by high PR-A levels, were 2.76 times more likely to relapse than patients with lower ratios, indicating resistance to tamoxifen.

CONCLUSIONS

This study suggests that knowledge of the PR-A:PR-B ratio may identify a subgroup of ER-positive/PR-positive patients with node-positive breast cancer that benefit poorly from endocrine therapy.

Progesterone receptor by immunohistochemistry and clinical outcome in breast cancer: a validation study

Progesterone receptor is a surrogate marker of estrogen receptor activity in breast cancer and its utility in helping predict clinical outcome has been established using biochemical assays. However, most laboratories worldwide have switched to immunohistochemistry to assess progesterone receptor, but unfortunately no validated immunohistochemical assay exists for progesterone receptor. The purpose of this study was to develop and validate an immunohistochemical assay for progesterone receptor in breast cancer. The assay was based on monoclonal antibody 1294 (DakoCytomation) and slides were scored microscopically using the 'Allred score' on a scale of 0-8. The assay was compared to ligand-binding assay in 1235 breast cancers, and a subset (n=362) that received only hormonal therapy was used to define a cutoff for progesterone receptor-positive. Clinical utility was validated in an independent set of samples (n=423) from a clinical trial randomizing premenopausal breast cancer patients to tamoxifen+oophorectomy vs observation following surgery. A cutoff of >2 (corresponding to >1% positive cells) dichotomized patients with significantly better or worse clinical outcome (P=0.0014). Progesterone receptor by immunohistochemistry provided significantly better results than progesterone receptor by ligand-binding assay in predicting clinical outcome. In the clinical trial, a positive result in univariate analyses was associated with significantly improved disease-free and overall survival both in untreated (hazard ratios/P=0.656/0.060 and 0.479/0.005, respectively) and hormonally treated patients (hazard ratios/P=0.529/0.017 and 0.451/0.007, respectively). Positive progesterone receptor remained significant for improved disease-free and overall survival (hazard ratios/P=0.666/0.038 and 0.549/0.007, respectively) in multivariate analyses including the standard variables of tumor size, nodal status, treatment, histological grade, and HER-2/neu status. Estrogen and progesterone receptors are codependent variables and progesterone receptor was a weaker predictor of response to endocrine therapy than estrogen receptor when both were included in multivariate analysis. This is the first comprehensive study assessing the clinical usefulness of progesterone receptor by immunohistochemistry in archival tissue in breast cancer. Progesterone receptor assessed by immunohistochemistry provides useful information about clinical outcome and it is better than progesterone receptor measured by ligand-binding assay.

Comparison of different antibodies for detection of progesterone receptor in breast cancer

Monoclonal antibodies directed against human estrogen receptor (ER) and progesterone receptor (PR) have been used extensively for biochemical and immunohistochemical detection of receptors independent of hormone-binding assays. These antibodies have been valuable both for experimental work and for detection of receptors in clinical breast cancer specimens. The purpose of this study was to characterize the sensitivity and specificity of different antibodies for detection of PR by immunohistochemistry (IHC) of formalin-fixed paraffin breast carcinoma sections. The panel of twelve antibodies included two new ones (PgR636 and PgR1294) produced prospectively to be resistant to formalin fixation and paraffin embedding. Fifty-nine breast carcinomas, having known PR levels by biochemical ligand-binding assay, were used to prepare multitumor paraffin-embedded tissue blocks for characterization of the PR antibodies. Of all the antibodies tested, both PgR636 and PgR1294 stained the highest percentage of breast carcinomas known to be positive by the biochemical assay (95-98%) and they exhibited the highest concordance with the biochemical assay (88-90%). The PgR636 and PgR1294 antibodies, along with one other, PR 88, also gave the highest intensity of nuclear staining, while PgR636 and PgR1294 stained the highest mean percentage of tumor cell nuclei. Antigen retrieval was not necessary for PR immunostaining by PgR636 and PgR1294 in most tumors and other tissues examined, but did slightly increase the staining intensity. The majority of the other antibodies tested were highly dependent on antigen retrieval; only PR 88 and KD 68 antibodies approached the performance of PgR636 and PgR1294 without antigen retrieval. These results indicate that PgR636 and PgR1294 are optimal antibodies for IHC detection of PR in routine paraffin tissue blocks.

Steroid Hormone Receptor Immunohistochemistry in Breast Cancer: Past, Present, and Future

This article reviews the development of steroid hormone receptor detection using the biochemical approach and the disadvantages inherent in these systems. The early history of methods for the in situ detection of receptors is related, culminating in the development of histologic immunoassays using monoclonal antibodies. Correlation of the latter with disease-free and overall survival and with clinical endocrine response are presented together with preliminary findings utilizing a new generation of antireceptor antibodies. Current problems with test scoring and interpretation are detailed with a section devoted to image analysis for assay quantification. Emphasis is placed on the fact that because so many different antibodies and tissue substrates have been employed in the past, these histologic receptor immunoassays cannot yet be considered to be fully validated. It is stressed that different laboratories must employ the same antibodies, substrates, detection systems and methods of scoring, and then correlate findings with measurable clinical end points. Only then can the assays be included in the brief list of approved breast cancer prognostic and predictive markers to eventually replace the routine biochemical methods of steroid receptor detection.

High sensitivity and specificity of immunohistochemistry for the detection of hormone receptors in breast carcinoma: comparison with biochemical determination in a prospective study of 793 cases

AIMS

The hormone receptor (HR) status of breast cancer is an important prognostic factor and predictive parameter of the response to hormone therapy. Enzyme immunoassay (EIA) is currently the standard for determination of HR, but immunohistochemistry (IHC) represents a potentially useful alternative. We used IHC to determine HR status in a large prospective study and compared the results to those obtained by EIA. This study was designed to determine which technique should be used in daily practice in our institution which manages a large number of patients.

METHODS AND RESULTS

Oestrogen (ER) and progesterone (PgR) receptor status was evaluated in a prospective series of 793 infiltrating breast cancers by IHC in paraffin-embedded tissue sections, using antibodies 6F11 and 1A6, with a rigorous quality control of the methodology. ER were found to be significantly expressed in 81% of cases after IHC analysis and in 78% of cases by EIA. For PgR, the respective rates of positivity were 65% and 69%. The tumour HR level detected by either technique was significantly correlated with the value of tumour size, histological grade and S-phase fraction. A significant link was observed between the percentage of labelled cells after IHC analysis and the amount of protein detected by EIA. Critical analysis of discordance found that, in the group of invasive lobular carcinomas, the rate of HR positivity was higher with IHC (84%) than with EIA (45%) and that, in the overall population, IHC was more specific than EIA, since cases with nonrelevant positivity related to intraductal normal or neoplastic cells expressing HR could be discarded. The cost of IHC analysis was found to be about one-third of that of EIA.

CONCLUSIONS

IHC is more sensitive, specific and economical than EIA. It should constitute the new standard technique provided that good quality assurance procedures are respected.