ESR1 and breast cancer: Using data from three highly overlapping sets of patients (N = 162 in total) with early‐stage estrogen‐receptor‐positive luminal BC—high‐coverage targeted DNA sequencing (113 genes), mRNA sequencing, and full micro‐RNA (miRNA) transcriptome microarrays—we describe complex oxysterol‐related interaction (correlation) networks, with validation in public datasets (n = 538) and 11 databases.