ESR1 and breast cancer: Triple-negative breast cancer (TNBC), defined by the absence of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2), accounts for approximately 25-30% of all breast cancers and exhibits poor prognosis and strong invasiveness (1) As the standard treatment strategy for early-stage TNBC, neoadjuvant chemotherapy (NAC) not only provides opportunities for breast conservation and sparing axillary lymph node dissection but also identifies patients with residual disease at high risk of relapse (2).