A quality control study to assess the inter-laboratory variability of routine estrogen and progesterone receptor assays

The steroid hormone receptor laboratories of Bern, Basel, Zürich, Locarno, Lausanne and Geneva have participated in a quality control study to assess potential inter-laboratory variability in results of tests for determination of steroid hormone receptor status in human breast tumor biopsies. Homogeneous breast tumor powders containing low, medium and high concentrations of estrogen receptors (ER) and progesterone receptors (PR) were prepared in Bern and dispatched on solid CO 2 to each laboratory within 1 day of preparation. Each laboratory was requested to assay each powder for ER and PR by their usual procedures. The results revealed that the quantitative discrepancies in ER and PR binding values among the participants could be attributed in part to variations in the methods used for measuring cytosol protein content and also to the differences in hormone receptor assay methods. Nevertheless, all of the laboratories were able to identify the samples containing low, medium and high concentrations of ER and PR.