Stabilization of human breast cancer progesterone (5020) receptor by sodium molybdate

Inclusion of the salt, sodium molybdate, at 20 mmol/l concentration during the determination of progesterone receptor in human breast cancer cytosols was associated in a number of samples with marked stabilization of binding by the radioactive ligand, 5020, to 8S and 4S receptors. Both the percent of positive patients and the absolute amount of PR were increased, with the appearance of 8S peaks where none had been evident in controls without the salt, and increased amounts of 8S and 4S binding in other samples. In addition, results from some dextran-coated charcoal assays were altered, and positive samples incubated in the presence of the salt frequently yielded higher values of PR. Finally, estrogen receptor values determined by SDG assays have been increased in the presence of the salt. Routine addition of sodium molybdate to samples analyzed for PR by centrifugation overnight can be expected to yield an increased percent of receptor-positive patients with higher average concentration of receptor, compared with results of previous methodology. Its presence during the dextran-coated charcoal assay can also alter the measured binding. Although the stability of ER during overnight centrifugation is greater, in some patients additional receptor can be detected when buffers include this salt.