The task force of the Japanese Breast Cancer Society was assembled to examine variable factors related to the immunohistochemical evaluation of hormone receptors in breast cancer, and to provide recommendations for adequate handling of specimens and accurate evaluations for hormone receptors. The various factors examined were: i) the adequate handling of breast cancer tissue for IHC, ii) the concordant rate between EIA and IHC assays using 5 different staining methods, iii) the inter-observer diversity for evaluation, and iv) the threshold for the predictive value of endocrine therapy of primary and recurrent/metastatic breast cancers. The conducted studies found that a 10% threshold was stable and reliable in spite of different validations including the concordance between IHC and EIA assays, inter-observer diversity and disease-free survival rates for patients who received tamoxifen for primary breast cancers. It was also found that 1% of threshold was useful in limited situations including the predictive value of endocrine therapy for recurrent/metastatic breast cancers. Based on these results for technical, pathological and clinical validation studies, a recommendation was proposed. Herein, we summarize the evidence, on which the recommendations were made, and customize the recommendations suitable for the current status.

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