Evaluation of an enzyme immunoassay for estrogen receptors in human breast cancers.

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 receptor-positive 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.