For more than 25 years, tamoxifen has been the gold standard for the endocrine treatment of all stages of oestrogen-receptor-positive breast cancer, and the World Health Organization lists tamoxifen as an essential drug for the treatment of breast cancer. It is estimated that more than 400,000 women are alive today as a result of tamoxifen therapy, and millions more have benefited from palliation and extended disease-free survival. Interestingly, tamoxifen also became the first cancer chemopreventive approved by the Food and Drug Administration (FDA) for the reduction of breast-cancer incidence in both pre- and post-menopausal women at high risk. However, 40 years ago, it was hard to imagine that a non-toxic targeted treatment for breast cancer could be developed at all.