found that exosomal miR-940 was mainly secreted by tumor cells in vivo through an analysis of exosomes and exosome-free supernatant from primary breast cancer cells and peripheral immune cells and revealed that miR-940 expression is increased in trastuzumab-sensitive HER2-positive metastatic breast cancer patients and further increased in trastuzumab-resistant patients (29). This evidence concerns the gene ERBB2 and breast cancer.