Human subjects: Patient-derived breast tumors (PDX (X. Zhang et al., 2013)) were obtained from Dr. Giorgio Inghirami and estrogen receptor positive (ER+) breast tumors were obtained from Dr. Eleni Andreopoulou at Weill Cornell Medicine under IRB-approved protocols (WCM 1410015560 and 1603017108). The gene discussed is ESR1; the disease is breast neoplasm.