Effects of molybdate on classification of estrogen and progesterone receptor status in human breast cancer.

Incorporation of disodium molybdate in the homogenization buffer for breast cancer specimens was shown to inhibit a time and temperature dependent loss of estrogen (ER) and progesterone (PR) receptor binding capacity in the cytosols. Since positive receptor values are correlated with response to endocrine therapy, the effect of molybdate incorporation on ER/PR classification was further investigated in two separate series of specimens. In one series of 75 consecutive specimens, ER and PR were analyzed before incorporation of molybdate in the assays, and the results compared with the next 75 consecutive specimens after incorporation of molybdate. The mean ages of the 2 groups of patients were not significantly different (59.1 +/- 13.4 versus 59.4 +/- 13.3 years). It was found that the PR binding capacity was significantly higher, the proportion of ER+/PR- specimens was significantly reduced, and that a bimodal distribution of ER+ specimens only became apparent when molybdate was incorporated in the ER and PR assays. The possibility exists that ER+ specimens with binding capacities above 175 fmol/mg protein, constituting 24% of all the specimens and representing the second bimodal peak, may represent hormone dependent tumours.