Transport of nanoparticles across the endothelial cell layer

•We here discuss how intravenously injected nanoparticles enter tumours and are taken up by tumour cells.•We discuss how nanoparticles can be transported across the endothelial cell layer.•More studies are required to conclude about the contribution of passive and energy dependant mechanisms for this transport. Studies of how intravenously injected nanoparticles (NPs) enter tumours and are taken up by tumour cells have been discussed for more than three decades. Despite this, we still have much to learn about interactions between NPs and how they can be transported across the endothelial cell layer. More studies are required before firm conclusions can be drawn regarding the contribution of passive or energy dependent mechanisms for transport of NPs over the endothelial cells allowing the NPs to reach solid tumours.