Relationships between oestrogen receptor, epidermal growth factor receptor, ER-D5, and P24 oestrogen regulated protein in human breast cancer

Proteins regulated by or related to the oestrogen receptor (ER) may prove to be more reliable indicators of prognosis and hormone sensitivity then expression of the receptor itself. It has been shown recently that expression of epidermal growth factor receptor (EGFR) is associated with a poor prognosis in breast cancer. In a series of 60 breast cancers, we have studied relationships between ER, ER‐D5 oestrogen receptor related protein, P24 oestrogen regulated protein, and EGFR using an immunohistochemical technique employing monoclonal antibodies in each case. In addition, radioligand binding assays for ER and EGFR were carried out and tumour histological grade was determined. Seventy‐one per cent and forty‐three per cent of tumours stained for ER‐D5 and P24, respectively, but there was no relationship between staining for these and ER or EGFR status. There was a significant correlation between staining for ER and EGFR, and the respective biochemical assays. Relating ER to EGFR, very few ER‐positive cases expressed EGFR, but this relationship fell short of significance. The prognostic significance of expression of the epitopes recognized by the ERD5 and P24 antibodies must await assessment of clinical outcome.