ESR1 and breast cancer: However, it is rare for TNBC patients to have long‐term survival due to tumor relapse after treatment.[3, 4] There is mounting evidence that a unique subpopulation of cancer cells exists in TNBC, referred to as breast cancer stem cells (BCSCs), which can be identified by aldehyde dehydrogenase 1 (ALDH1).[4, 5] BCSCs exhibit resistance or no response to conventional chemotherapeutic agents, radiation, and ER‐, HER2‐ or PR‐targeted drugs, consequently resulting in tumor relapse.[6] Hence, developing efficient strategies to eradicate BCSCs is an unmet demand for TNBC treatment.