Enzyme immunoassay of progesterone receptor in breast cancer biopsy samples. A comparison with the dextran coated charcoal method.

Progesterone receptor was measured in 97 breast cancer biopsy samples with two methods, the multiple point dextran coated charcoal method with Scatchard analysis and enzyme immunoassay. The measurable amount of progesterone receptor was usually higher with enzyme immunoassay (mean increase 30%). When comparing the two techniques quantitatively a high correlation coefficient was obtained (rs=0.88; p less than 0.001). A concordance in terms of progesterone receptor positivity and negativity was obtained in 81 of the samples (84%) when using 10 fmol/ml as the borderline value. If instead the cut-off value used for clinical evaluations at our laboratory (30 fmol PgR/mg protein) was applied, the concordance increased to 94%. The lack of concordance in the remaining samples may be due to difficulties in the interpretation of the Scatchard plots, especially at low receptor concentration levels and to differences in specificity between the two methods in certain samples. One obvious advantage with enzyme immunoassay compared to the dextran coated charcoal method is that significantly less tissue is needed.