1. ¹Department of Surgery, Christie Hospital NHS Trust, Manchester M20 4BX, USA
2. ²Clinical Research Department, Christie Hospital NHS Trust, Manchester M20 4BX, USA
3. ³CR-UK Department of Medical Oncology, Christie Hospital NHS Trust, Manchester M20 4BX, USA
4. ⁴University Department of Medical Genetics and Regional Genetics Service, St Mary's Hospital, Manchester M13 0JH, USA

Correspondence: Dr RB Clarke, Breast Biology Group, University of Manchester, Christie Hospital NHS Trust, Wilmslow Road, Manchester M20 4BX, UK; E-mail: rclarke@picr.man.ac.uk

⁵These authors contributed equally to this work

⁶Current address: Cancer and Infection Bioscience, AstraZeneca, Mereside, Alderley Park, Macclesfield, Cheshire SK10 4TG, USA

Received 27 October 2005; Revised 8 February 2006; Accepted 8 February 2006; Published online 14 March 2006.

Abstract

There is considerable interest in whether anti-oestrogens can be used to prevent breast cancer in women bearing mutations in the BRCA1 and BRCA2 genes. The effects of oestradiol (E₂), tamoxifen (TAM) and fulvestrant (FUL) on proliferation and steroid receptor expression were assessed in normal breast epithelium taken from women at varying risks of breast cancer and implanted into athymic nude mice, which were treated with E₂ in the presence and absence of TAM or FUL. Tissue samples were taken at various time points thereafter for assessment of proliferative activity and expression of oestrogen and progesterone receptors (ER and PgR) by immunohistochemistry. Oestradiol increased proliferation in the breast epithelium from women carrying mutations in the BRCA1/2 genes, those otherwise at increased risk and those at population risk of breast cancer. This increase was reduced by both TAM and FUL in all risk groups. In the absence of E₂, PgR expression was reduced in all risk groups but significantly more so in the BRCA-mutated groups. Subsequent E₂ treatment caused a rapid, complete induction of PgR expression in the population-risk group but not in the high-risk or BRCA-mutated groups in which PgR induction was significantly delayed. These data suggest that the mechanisms by which E₂ induces breast epithelial PgR expression are impaired in BRCA1/2 mutation carriers, whereas those regulating proliferation remain intact. We conclude that early anti-oestrogen treatment should prevent breast cancer in very high-risk women.