Endocrine therapy has now been used as an effective treatment for breast cancer for 100 years. It was the first successful systemic treatment for cancer, initially becoming accepted following George Beatson's (1896) observations that, in a proportion of pre-menopausal women with advanced breast cancer, bilateral oophorectomy resulted in disease regression. Over the subsequent 75 years, several other endocrine therapies for breast cancer were developed, including other surgical approaches to hormone ablation therapy such as adrenalectomy (Huggins & Dao 1953) and hypophysectomy (Luft & Olivecrona 1953), and hormonal additive therapies, such as the use of pharmacological doses of androgens, oestrogens, progestogens and glucocorticoids. However, as none of these approaches led to a significant improvement in the rates of tumour regression, clinicians' enthusiasm in the 1960s and early 1970s became focused on the use of newly developing cytotoxic chemotherapy regimens. Then, in the 1970s, tamoxifen, and subsequently a range of other new endocrine agents, became available which were of low toxicity and generally well tolerated - high-dose oestrogens were quickly replaced by tamoxifen, and adrenalectomy by aromatase inhibitors. Measurement of hormone receptor levels also became available, allowing better selection of patients whose tumours might be hormonally responsive. In addition, some of the limitations of cytotoxic drugs in breast cancer were starting to become apparent.