Endocrine therapy forms the backbone of treatment of ER+ breast cancer, and includes selective oestrogen receptor modulators (e.g., tamoxifen), selective oestrogen receptor degraders (e.g., fulvestrant), aromatase inhibitors (e.g., letrozole, anastrazole, exemestane) and ovarian function suppression (e.g., goserelin). The gene discussed is ESR1; the disease is breast cancer.