Measurement of progesterone receptors in human breast tumors: Comparison of various methods of analysis

Progesterone receptors in human breast tumors were measured by three separate methods. Cytosol prepared freshly from each tumor was analysed simultaneously by the single-saturating dose analysis, the sucrose density gradient method, and by the multi-point Scatchard plot analysis. Results from 10 individual tumors allows the following conclusion be made: (1) The data clearly demonstrate an excellent agreement between all three methods for the determination of total (4s + 8s) progesterone receptor concentration. No loss in receptor binding activity is observed during the time required for sucrose density gradient analysis. (2) Although the progesterone receptor exists as two macromolecular forms (4s + 8s), both have similar (if not identical) K Ds because receptor concentrations calculated by extrapolation of Scatchard plots are identical to those obtained from either the summation of 4s and 8s areas of sucrose gradients, or single-saturating dose assays. This finding supports the contention that all three methods can be used interchangeably in the clinical laboratory.