Comparison of enzyme immunoassay and dextran-coated charcoal techniques for progesterone receptor determination in human breast cancer cytosols.

We have compared a new enzyme immunoassay for progesterone receptors (Abbott PgR-EIA, monoclonal) with our standard radioligand binding-assay (PgR-RBA). For both assays cytosols were freshly prepared from human breast cancer specimens that had been stored frozen for up to 1 year, and predominantly tissues were used which contained critically low amounts of progesterone receptors. A highly significant correlation was observed between the PgR-EIA and PgR-RBA (Spearman: Rs = 0.85, n = 100). Using a cut-off point of 10 fmol PgR/mg protein, 87% of the values were in accordance with each other (52% negative, and 35% positive in both assays), whereas 13% scored positive (median: 16, range 11-38 fmol PgR/mg protein) in one assay and negative (median: 7, range 0-10 fmol PgR/mg protein) in the other. Also in cytosols from human ovarian and endometrial carcinoma tissues immunoreactive PgR could be detected, and significant correlations with PgR-RBA were observed (Rs = 0.94, n = 6) for both tissues.