Oestrogen receptor activation and molecular forms in human breast cancer

The oestrogen receptor (ER) present in human breast cancer cytosol was resolved by high performance size exclusion chromatography into a high molecular weight form (300 kDa) either alone or together with a lower molecular weight species (60 kDa). In tumours that contained the 60 kDa species there was a significant increase both in ER activation, determined by binding to oligo(dT)-cellulose, and the concentration of progesterone receptor (PR). Despite cytosolic ER being a potential homogenisation artefact, qualitative differences observed in vitro may reflect aspects of tumour biology in vivo.