It has been reported that microRNAs (miRNAs) are the most abundant macromolecules in exosomes, and exosome‐mediated miRNA delivery is widely believed to contribute to drug resistance in many cancers.[22, 23, 24] Therefore, we investigated whether CD63+ CAF‐derived exosomal miRNAs could induce ERα downregulation in BCs. Here, ESR1 is linked to cancer.