CA9 and renal cell carcinoma: Alternatively, recent studies have shown that CAIX-containing exosomes released by hypoxic renal cell carcinoma cells are taken up by HUVEC and promote migration and tube formation by human umbilical vein endothelial cells (HUVEC) in angiogenesis assays in vitro [34], raising the interesting possibility that CAIX-positive tumor cells may give rise to CAIX-containing exosomes in the tumor microenvironment of TNBC, offering an additional CAIX positive target for inhibition.