CYP19A1 and breast cancer: Original articles published in the last two decades have been searched in PubMed, using the following search terms: “extracellular vesicles and breast cancer”, “extracellular vesicles and endocrine resistance”, “extracellular vesicles and tamoxifen resistance”, “extracellular vesicles and aromatase inhibitor resistance”, “extracellular vesicles and estrogen receptor down regulators”.