For many years, tamoxifen has been the optimal form of endocrine (hormonal) therapy for breast cancer, and women who have oestrogen positive tumours (i.e. the cells express the oestrogen receptor on their surfaces) have derived disease free survival/survival advantages by taking this medication for five years after mastectomy. In a recent trial called the ATAC (anastazole/arimidex, tamoxifen or combined) trial, 9,000 post-menopausal women were randomised to take anastrazole, tamoxifen or both adjuvantly (after mastectomy or equivalent). After a median follow up of 2.5 years, there was a significantly lower recurrence rate in the patients treated by anastrazole compared with tamoxifen or the combination. The follow up is short and tamoxifen has a fantastic 'pedigree' having been studied in tens of thousands of patients for decades of follow up, so it would be premature to decide to wholesale swap tamoxifen for anastrazole but for sure the trial has produced a very interesting result that will be much debated. For example, the patients with Oestrogen receptor positive and HER-2 receptor positive tumours may the ones that derive a greater advantage from anastrazole.