Comparison between single saturating dose ligand binding assay and enzyme immunoassay for low-salt extractable oestrogen and progesterone receptors in breast cancer: a multicentre study.

An excellent correlation between ligand binding assay (LBA) and enzyme immunoassay (EIA) for both oestrogen (ER) and progesterone (PR) receptors has been reported. Nevertheless, considering that the clinical value of any discrepancy between LBA and EIA probably varies with the receptor level, we undertook a collaborative study in which a single saturating dose (SSD) LBA and EIA were compared in different ER and PR dose ranges. The values of ER measured by EIA were higher in tumours with low or intermediate receptor content, causing a misclassification of ER status in 9% of cases (ER+: 77.5%, EIA, 68.8% SSD). In the case of ER, EIA values tended to be higher than SSD in all centres. For PR, EIA and SSD were generally more comparable (PR+: 66.0% EIA, 72.0% SSD, discordance rate 6%), with EIA showing, however, different trends in different centres. PR concentration was not significantly different in ER SSD-/EIA+ and in ER SSD+/EIA+ cases, suggesting that EIA detects at least in part integer ER. We conclude that although EIA may be a reliable methodological alternative to SSD, the two methods are not interchangeable until effective cut-off levels for clinical decisions are assessed for EIA.