Twenty years of experience with the steroid receptor external quality assessment program - the paradigm for tumour biomarker EQA studies. On behalf of the EROTC Receptor and Biomarker Study Group.

Estrogen receptor (ER) 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 progesterone receptor (PgR)-assays have been evaluated in quality assessment studies for almost 20 years by the EORTC Receptor and Biomarker Study Group. This study analyses our findings over these years and concludes with a recommended minimum structure on which QA schemes for any biomarker could be based.