Background: Triple-negative breast cancer (TNBC) accounts for 15-20% of breast cancers but is responsible for a disproportionate number of deaths. We investigated the relevance, in TNBC, of nano-sized exosomes expelled from cells. Specifically, we compared effects of exosomes derived from the claudin-low TNBC cell line Hs578T and its more invasive Hs578Ts(i) 8 variant, as well as exosomes from TNBC patient sera compared to normal sera. Methods: Exosomes were isolated from conditioned media (CM) of Hs578T and Hs578Ts(i) 8 cells and from sera by filtration and ultracentrifugation. Successful isolation was confirmed by transmission electron microscopy and immunoblotting. Subsequent analysis, of secondary/ recipient cells in response to exosomes, included proliferation; motility/migration; invasion; anoikis assays and endothelial tubule formation assays. Results: Hs578Ts(i) 8 -exosomes versus Hs578T-exosomes significantly increased the proliferation, migration and invasion capacity of all three recipient cell lines evaluated i.e. SKBR3, MDA-MB-231 and HCC1954. Exosomes from Hs578Ts(i) 8 cells also conferred increased invasiveness to parent Hs578T cells. Hs578Ts(i) 8 -exosomes increased sensitivity of SKBR3, MDA-MB-231 and HCC1954 to anoikis when compared to the effects of Hs578T-exosomes reflecting the fact that Hs578Ts(i) 8 cells are themselves innately more sensitive to anoikis. In relation to vasculogenesis and subsequent angiogenesis, Hs578Ts(i) 8 -exosomes versus Hs578T-exosomes stimulated significantly more endothelial tubules formation. Finally, our 0959-8049/$ -see front matter Ó