1. ¹Breast Unit Research Group, University of Edinburgh, Western General Hospital, Edinburgh EH4 2XU, UK
2. ²MRC Human Reproductive Sciences Unit, Centre for Reproductive Biology, 49 Little France Crescent, Edinburgh EH16 4SB, UK

Correspondence: Professor PTK Saunders, E-mail: p.saunders@ed.ac.uk

Received 25 August 2005; Revised 8 February 2006; Accepted 27 February 2006; Published online 18 April 2006.

Abstract

In order to elucidate the relative importance of oestrogen receptor (ER), ER and an ER variant (ER2/cx) in the response of breast cancers to tamoxifen, tumour levels of each receptor were assessed in 36 patients before and after 3 months of neoadjuvant treatment with tamoxifen (20 mg daily). All patients were postmenopausal women presenting with large ER-positive breast cancers. Clinical response to treatment was assessed by tumour volume changes as determined from sequential ultrasounds and pathological response by comparison of the tumour morphology before and after treatment. Of 33 cases, 23 (70%) were classified as having a clinical response and 16 (48%) as having a response pathologically. All tumours stained positively for ER and ER and 15 out of 33 (45%) for ER2/cx. There were no significant differences in quantitative expression of any receptor between tumours that subsequently responded and that did not, whether response was assessed clinically or pathologically. Tamoxifen treatment was associated with a decrease in ER, but an increase was the most frequent change (17 out of 33) in ER, and no consistent change was evident in staining of the ER2/cx variant. In summary, ER1 and ER2/cx variant protein are detected in ER-positive breast tumours but their expression is not associated with a response to tamoxifen. Differential changes in ER and ER were seen with treatment.