How best to express oestrogen receptor activity.

Oestrogen receptor (ER) activity, detected and expressed in a variety of ways, is important in breast cancer. Experience in Edinburgh (1973-1996) showed that [1] no single mode of expression was entirely satisfactory, [2] the probability of a good 'outcome' (prognosis or response to endocrine therapy) increased with increasing activity (either fmol ER sites/mg protein or per cent cells staining for ER). Thus the use of a single 'cut-off' should be avoided and activity quantified, or stratified into categories.