Prognostic Usefulness of Estrogen Receptor Iimminocvtocheniical Assays for Human Breast Cancer1

Breast cancers of postmenopausal patients at high risk for recurrence participating in an adjuvant therapy protocol were independently assayed for estrogen receptor by conventional dextran-coated charcoal steroid binding assays and by ¡mmunocytochemistry (ER-ICA) to compare the two assays and to assess the prognostic usefulness of ER-ICA. The ER ICA was based on a monoclonal antibody to the estrogen receptor and was applied to lightly fixed, frozen sections of the cancers. Excellent agreement was found between the two estrogen receptor methods. It was found that a combination of the distribution of ER-ICA stained cells and the overall staining intensity gave a statistically significant correlation with the quantitative estrogen receptor dextran-coated charcoal steroid binding assay value. In addition, the overall appraisal of the lesion as ER-ICA positive or negative as well as the ER-ICA staining intensity and proportion of ER-ICA stained cancer cells related to patient diseasefree interval and survival, independent of patient lymph node involvement. This relationship of ER-ICA status to prognosis appeared not to relate only to responses to adjuvant tamoxifen treatment since it also was observed with patients who did not receive the antiestrogen.