Measurement of oestradiol receptors by five institutions on common tissue samples.

The soluble oestrogen-receptor content of common breast tumours has been measured by 5 different laboratories, each using their own assay procedure. Good agreement was achieved on whether a sample was positive or negative for oestrogen receptor. Qualitative differences between laboratories could be explained by differences in thiol-reagent content of assay medium and by the method of homogenization. Recommendations are made on some of the factors involved in the routine assay of receptors in breast tumours.