Enzyme immunoassay of estrogen receptors in fine needle aspirates of breast tumors.

Enzyme immunoassay of estrogen receptors (ER-EIA) was compared to radioligand assay (ER-RLA) in fine needle aspirates of breast tumors. Fine needle aspiration is a relatively atraumatic means of harvesting malignant cells from breast tumors. Fine needle aspiration provides a homogeneous suspension (about 90% malignant cells) with a sufficient amount of cellular material (10 to 50 micrograms DNA per sample) for single point radioligand assays of extractable estrogen (ER) and/or progesterone receptor (PR) in about 85% of primary adenocarcinomas at the time of diagnosis. Sixty-one different samples of malignant mammary cells were obtained by fine needle aspiration from 43 adenocarcinomas, 11 metastatic axillary nodes or 7 cutaneous nodules. Thirteen patients were under antiestrogen therapy (tamoxifen). ER-EIA was performed with Abbott's reagents, following the manufacturer's protocol. ER-RLA was a single saturation (5 nM) dextran-charcoal assay with [3H]R2858 as the labeled estrogen. The sensitivity of ER-EIA allowed dilution of the sample up to 10 times (according to sample cellularity and ER level) with less than 20% deviation from undiluted samples. Three levels of dilution of the samples (1/1, 1/2, and 1/10) allowed them to fall at least once into the range of the ER-EIA standard curve. Quantitative correlation between ER-EIA and ER-RLA was high (r = 0.86), and highest (r = 0.97) when samples from patients undergoing tamoxifen treatment were excluded. Major discrepancies between ER-EIA and ER-RLA appeared in those patients undergoing tamoxifen therapy; much higher values were obtained by ER-EIA. Eight of 13 of these patients were ER negative by ER-RLA but ER positive by ER-EIA. This preliminary observation indicates that in vivo ER modulation by hormones and antihormones should be reevaluated.