Reliability of steroid hormone receptor assays: an international study

The reproducibility of oestrogen and progestin receptor assays performed by laboratories participating in an international breast cancer treatment trial has been assessed. Three tissue reference powders containing low, medium and high oestrogen receptor levels (22 ± 4, 88 ± 7, 227 ± 13 fmol/mg cytosol protein respectively) were prepared in Louisville, KY, U.S.A., assayed repeatedly and multiple samples of each shipped on solid CO₂ to the coordination-distribution centre in Berne, Switzerland. Samples were dispatched from Berne to Cantons within Switzerland, to Yugoslavia, South Africa, Australia, New Zealand and also back to the United States for oestrogen and progestin receptor assays. Results were returned to Berne, Switzerland. There was a decrease in the levels of oestrogen and progestin receptors during the time of storage and transit. However, the ability to assign a powder to either the low, medium or high level of oestrogen receptor was not affected. Laboratories also determined progestin receptor. All laboratories clearly identified the powder containing the low level of progestin receptor, but there was poor quantitation with the other two assay standards. It is recommended that clinical hormone receptor laboratories, especially those participating in clinical trials, establish regular quality control procedures for both daily evaluation internally and periodic outside monitoring of interlaboratory variation.