Assay of estradiol receptors in human breast carcinomas using the gamma emitting ligand 16 alpha [125I]iodoestradiol.

Estradiol receptors (ER) were measured in human breast carcinomas using the gamma emitting ligand 16 alpha [125]iodoestradiol. Competition experiments with excess unlabeled steroids showed that the iodoestradiol was bound specifically by the ER. The K4 of the iodo and tritium-labeled estradiol for the receptor were similar with values of 3.4 x 10(-18) M and 2.1 x 10(-10) M respectively. A comparison of ER determination in 25 human breast carcinomas using both [3H]estradiol and [125I]estradiol gave a correlation coefficient value of 0.97. It is concluded that the use of [125I]estradiol should greatly simplify the ER assay and facilitate its introduction into the routine hospital laboratory.