Estrogen receptor measurement in low-protein breast cancer cytosols. A modified charcoal technique.

The assay of estrogen receptor (ER) in human breast cancer biopsies is usually excellent using the dextrancoated charcoal method. If the cytosol protein concentration is below 1 mg/ml, however, underestimation of ER content occurs presumably due to adsorption of ER to the charcoal. This problem can be minimized if 1 mg/ml of bovine serum albumin (BSA) is added to the charcoal solution prior to use.