A recent study by Rakha et al1 shows that breast tumours with single hormonal receptor positivity are biologically and clinically distinct groups and particularly that oestrogen receptor (ER)-negative/progesterone receptor (PR)-positive tumours exhibit more aggressive behavioural characteristics than double-receptor-positive tumours. However, there is also an increasingly prevalent opinion, that the ER−/PR+ phenotype does not exist and that the ER-negativity in these cases is due to inadequate tissue fixation or technical failure of the immunohistochemical assay.2^–4

This is an important dichotomy to resolve because, if ER−/PR+ tumours simply represent an artefact of the method of assessment, then they are essentially positive for both the receptors, which may have implications for how these patients are managed. To investigate this, we reviewed data from …