EORTC external quality assurance program for ER and PgR measurements: trial 1998/1999. European Organisation for Research and Treatment of Cancer

Steroid receptor assays have clinical relevance in selecting women who would benefit from endocrine intervention. As the degree of benefit from endocrine therapy is directly related to the quantity of receptor present in the tumour, the quality of the steroid receptor assays is important. Moreover, since patients entered in multi-centre trials often include stratification based on the receptor status, receptor assays should be comparable between different institutes. ER- and PgR-assays have been evaluated in quality assessment studies for almost 20 years by the EORTC Receptor and Biomarker Study Group. During the QA trial 1998/1999 results were reported by 42 participants performing the Ligand Binding Assay (LBA) and by 39 participants using the Enzyme Immuno-Assay (EIA) kit. Each participant received a set of 12 QA vials to be analysed two at a time at two-monthly intervals. The between-laboratory CVs of ER LBA and EIA amounted to 40-50%. For PgR the between-lab CVs for the EIA method are lower as compared with LBA but still are approx. 30%. Notwithstanding the high deviation in reported values and the high between-lab CVs, the consistency of the participants over the year is acceptable, which pave the way for calibration. Indeed, after normalization of assay results the mean between-lab CVs dropped to 11% for ER LBA, 14% for ER EIA, 9% for PgR LBA and 11% for PgR EIA. Such a reduction of between-laboratory CVs is an essential requirement for the use of steroid receptor data in multicentre clinical studies.