Evolution of endocrine adjuvant therapy for early breast cancer

Endocrine treatment plays a pivotal role in the adjuvant therapy of patients harbouring oestrogen and/or progesterone receptor positive breast cancer. The objective of this paper is to critically review endocrine treatment options in early breast cancer focusing on ongoing development. Literature was collected through the ISI Web of Science and PubMed in January/February 2009 with subsequent update by December 2009, using the words breast cancer, endocrine therapy, oestrogen receptor and aromatase. Endocrine therapy improves outcome in early breast cancer. Yet several controversies remain. There has recently been a lack of general consensus regarding the limit of oestrogen receptor positivity. As for adjuvant therapy in general and use of aromatase inhibitors in particular, we need the results from ongoing studies to decide what may be the optimal duration of therapy and regimen (sequential treatment versus monotherapy; one drug compared with another). Further, there is a need to critically assess optimal use of endocrine therapy for metastatic disease among patients previously exposed to endocrine regimens in the adjuvant setting. While in general the mechanisms of resistance to endocrine therapy among ER positive tumours remains unknown, merging evidence suggest a role of different growth factor pathways, in particular HER-2 activation. Thus, particular attention is paid to the topic of HER-2 expression as a potential cause of endocrine resistance.