ESR1 and breast carcinoma: Based on molecular classification, triple‐negative breast cancer (TNBC), which lacks expression of estrogen receptor (ER), progesterone receptor (PR), and Her2, accounts for ≈12–17% of breast cancer.[qv: 2] Patients with TNBC have a relatively poorer prognosis compared with those with other breast cancer subtypes; this is due to its aggressive clinical properties and lack of established molecular targets for therapy.[qv: 3] Therefore, there has been an intense interest in finding new medications that can treat TNBC.