This article traces the development of modern day breast cancer treatment from 1896 when observations were made on the positive response of patients to oophorectomy. The oestrogen receptor was defined and tamoxifen was discovered to be an effective anti-oestrogen. The genes related to breast cancer, BRCA1 and BRCA2, were found to confer high risks of breast and ovarian cancer on women with these genes. The application of functional genomics to breast tumours would result in a more accurate classification of cancers and hopefully more specific therapy and better clinical outcomes. An important off-shoot of anti-oestrogen research has resulted in a new class of drugs called selective oestrogen receptor modulators for treatment of osteoporosis and dyslipidemia.