ESR1 and cancer: Our normal samples consisted of two cell lines and two primary tissues, and our breast cancer samples included 13 primary human breast tumor biopsies [three hormone-positive, ER+/PR+; three HER2+; and seven triple-negative, TNBC (triple negative breast cancer)], nine patient-derived xenograft (PDX) tumors, and four cancer cell lines (Fig. 1A and file S1).