Criteria for the Establishment of a Double-Labeling Assay for Simultaneous Determination of Estrogen and Progesterone Receptors

Abstract

The availability of [125I]-16.alpha.-iodo-3,17.beta.-estradiol ([125I]-E2), with binding characteristics similar to estrogen receptor (ER), enabled the establishment of a double-labeling assay for the simultaneous determination of ER and progesterone receptors (PgR) using 125I-E2 and [3H]-R5020 [promegestone]. The criteria for the establishement of such a double-labeling assay are described. Human mammary tumor cytosols were investigated with the standard routine receptor assay for ER as well as PgR, and the results were compared to those obtained by the double-labeling assays. For ER: r = 0.691 and the parameters of the regression line were Y = 1.025 .times. X-0.036. When referring to the standard assay, 3 determinations were false-positive and 4 false-negative. For PgR: r = 0.984 and the parameters of the regression line were Y = 0.960 .times. X + 12.16. One value was false-negative and 1 false-positive. An equivalence of the 2 methods could be demonstrated. This new assay reduces by half the amount of tissue necessary for a valid 4- to 6-point saturation analysis, the time required for performing the assay and its cost. [Determination of ER and PgR has been of value in the selection of breast cancer patients for either endocrine or cytostatic therapy.].