Improved method for assay of estradiol and progesterone receptors with special reference to breast cancer

Isoelectric focusing of estradiol receptor (ER) and multiple point dextran-coated charcoal (DCC) technique for progesterone receptor (PgR) were adapted for assay of both receptors in the same cytosol sample. Technical improvements and increased recovery of receptors were achieved. 1.0 fmol/ml cytosol of ER may be detected; sensitivity of PgR was 5-10 fmol/ml cytosol. Quantitation of ER was made in 414 (95%) out of 434 consecutive breast cancers. Inclusion of isoelectric focusing records showing only qualitative indication for presence of ER resulted in 98% ER containing tumours, supporting the aspect that strictly ER negative tumours are a rarity. Implications for therapy in disseminated disease are discussed.