Endocrine therapies for the treatment of HR+/HER2− advanced BC include tamoxifen, the selective estrogen receptor modulator; nonsteroidal and steroidal aromatase inhibitors (AIs), which inhibit the peripheral synthesis of estrogen, thereby reducing estrogen levels (eg, anastrozole, letrozole, and exemestane); fulvestrant, the selective estrogen receptor downregulator (SERD).5, 8. The gene discussed is ESR1; the disease is breast cancer.