Measurement of progesterone receptor in human breast cancer biopsies.

Abstract

An improved sucrose gradient procedure for measuring progesterone receptor (PR) status was compared with other methods in an attempt to improve the assay of PR, a possibly important determinant in predicting endocrine therapy responses. Tritiated 3H-labeled R 5020 PR assay was modified to determine the actual nature of the competitive binding detected using sucrose density gradient centrifugation. An underestimation of 8S receptor was the result when using the swinging bucket technique, perhaps due to the prolonged run time (16 hours) involved. Hence, a vertical tube rotor was used which eliminated the problem. The 4S component was shown not to be PR, but probably an aberration due to failure to adsorb to hydroxylapatite. Dextran-coated charcoal and hydroxylapatite Scatchard plots confirmed this aberrant finding in that values derived from these methods correlated well with the 8S component of the gradient profile and not with the sum (8S + 4S) in a series of 27 human breast cancer specimens. In the same series the use of dextran-coated charcoal or hydroxylapatite single-saturating-dose assays correlated well with the 8S component of sucrose gradients. However, it is cautioned that until more experiments with these types of correlations are compiled, the 8S component of sucrose density gradient profiles as obtained from vertical tube rotor centrifugation yields the most reliable data on PR concentrations in human breast tumors.