Endocrine therapy is now established as the treatment option of choice for postmenopausal women with hormone receptor-positive advanced breast cancer. The benefit of the third-generation aromatase inhibitors (AIs) in this setting has prompted their evaluation in the treatment of early breast cancer. This article reviews the current clinical status of AIs as adjuvant therapy for early-stage breast cancer in postmenopausal women, focusing on the largest adjuvant breast cancer study till date to provide data, the ‘Arimidex’, Tamoxifen, Alone or in Combination (ATAC) trial.

This article examines the experimental and clinical evidence of the effect of growth factor signalling in an attempt to reconcile the seeming paradox of, on the one hand, evidence that growth factor signalling can facilitate the activity of oestrogen receptor-α (ER-α), and on the other hand, evidence that extreme growth factor signalling can promote loss of ER function and expression, thereby promoting an endocrine insensitive and ultimately ER− phenotype. The results of this analysis lead to the therapeutic possibility that ER negativity may, in some instances, be reversible to generate endocrine response and improve patient prognosis.