In his report of February 1974, Walpole wrote: “By good fortune, Nolvadex was launched at a time of increased interest in the assessment of the endocrine status in breast cancer51.” Tamoxifen was shown to be highly effective in binding to the estrogen receptor and, before long, researchers in Europe and the US were therefore using tamoxifen as a tool to “predict the response of breast tumors to hormone therapy52.” However, this new use for tamoxifen brought out the fact that not all patients whose tumors had demonstrable estrogen receptor levels responded well to endocrine therapy. The gene discussed is ESR1; the disease is breast neoplasm.