Five years of adjuvant treatment with tamoxifenimproved clinical outcome compared to shorter adjuvant therapy (EBCTCG 1998), and for more than a decade, 5 years of adjuvant tamoxifen(Davies et al. 2011) (oraromatase inhibitors, AIs) was the standard of care for ER+ breast cancer. The gene discussed is ESR1; the disease is breast carcinoma.