It is now almost 40 years since it was first shown that oestrogenic hormones exert their actions through combination with specific receptor proteins.¹ Subsequently, endocrine responsive breast cancers were shown to contain increased amounts of these oestrogen receptors (ER).² There is almost worldwide acceptance that the measurement of oestrogen and progesterone (PR) receptors provides valuable information to aid in the selection of patients for endocrine treatment.³ Furthermore, the recent overview of randomised trials of antihormone treatments in early breast cancer has confirmed this,⁴ and has recognised the need for some degree of quantification, because benefit is proportional to the amount of the receptor …