For 22 out of 23 patients with WES and/or RNA-seq of a baseline biopsy (n = 22/23, 96%), we identified genomic or transcriptomic features that could explain the tumor’s resistance to CDK4/6i or anti-ER treatments (Fig. 4, Supplementary Fig. 3, Supplementary Data 6). Here, ESR1 is linked to neoplasm.