Quality control study for estradiol receptor determination.

Lyophilized calf uterine cytosol standards for estradiol receptor (ER) were prepared separately in two institutes. The ER binding capacity was determined by dextran-coated charcoaL (DCC)-technique using a multi-point Scatchard analysis. The intra- and inter-assay coefficient of variation determined on the Hungarian preparation were 13.10% and 14.70%. The dissociation constant (Kd) values of all the samples ranged between 1.2 X 10(-9) M and 9.35 X 10(-10) M. Standards stored at--70 degrees C and at 0-4 degrees C proved to be stable for several months. At ambient temperature, a progressive decline of the ER activity was observed during a 1 year storage period. The use of the lyophilized calf uterine cytosol standards stored at 0-4 degrees C is recommended for both intra- and inter-laboratory quality control study in multicentric clinical trials of breast cancer.