ERBB2 and cancer: To test the hypothesis that exosome-delivered miR-HER2-E1 has tumoricidal effects on HER2-dependent cells by blocking replenishment of the protein in HER2-positive SK-OV-3 and HCT116 cancer cells as well as in HER2-negative MDA-MB-231 and HEp-2 cancer cells (Additional file 1: Fig. S2), the four cell lines were exposed to 1 μg of exosomes purified from HEK-293 cells transfected with miR-HER2-E1 respectively.