MKI67 and breast cancer: Han et al. (2020) have confirmed that exosomes can reverse the resistance of trastuzumab in BC by delivering miR-567. To further verify the effect of miR-224-5p carried by exosomes on BC cell survival, MTT, colony assay and flow cytometry were performed. And the results demonstrated that hUCMSCs-exo could transport miR-224-5p into MCF-7 and MDA-MB-231 cells to promote the proliferation and survival of cancer cells and inhibit the decrease of their apoptotic rate. Ki-67 protein is a marker of tumor proliferation (Menon et al., 2019).