ESR1 and breast cancer: Conventional bioinformatic predictions using TargetScan and DIANA micro-T [31] failed to detect any miR-4728-3p CS target sites in ESR1 and deep sequencing of HER2+ BC tumors showed no evidence of 5′-end truncated isomiRs (Fig. 1C), so we searched our AGO-CLIP data for support for an IS-ESR1 interaction.