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Evaluation of an Enzyme Immunoassay for Estrogen Receptors in Human Breast Cancers¹

Tenovus Institute for Cancer Research, University of Wales College of Medicine, Cardiff, United Kingdom CF4 4XX [R. I. N., P. C., A. B. F., R. K., P. F., K. G.], and Department of Surgery, City Hospital, Nottingham, United Kingdom NG5 1PB [M. W., C. W. E., R. W. B.]

An estrogen receptor enzyme immunoassay kit (ER-EIA) has been evaluated in 70 human breast carcinomas against a routine cytoplasmic [³H]estradiol binding assay (ERU). A linear correlation between the ER-EIA and the ERU was observed for binding values up to 400 fmol/mg of cytosol protein. Above this value, the ERU underestimates the concentration of receptor. The ERU gave a lower number of estrogen receptorpositive tumors (50 of 70) than did the ER-EIA assay (59 of 70). In the ERU-negative ER-EIA-positive tumors, receptor values as determined by the ER-EIA assay all fell below 50 fmol/mg of protein (mean, 19.9 ± 4.2 fmol/mg of protein). Application of an exchange procedure which estimates the total steroid binding capacity of the cytosol gave positive results in 7 of 9 ERU-negative ER-EIA-positive tumors (mean, 16.9 ± 2.95 fmol/mg of protein). Subdivision of the binding data according to the menopausal status of the patient indicates low receptor values in premenopausal women by each assay. A correlation between the ER-EIA assay and the histological grade of tumors was observed; Grade I well-differentiated tumors were all positive, while Grade II and III tumors were 86% and 75% positive, respectively. No correlation between the ER-EIA assay and tumor lymph node stage or tumor size was observed.