These plasma vesicles may originate from cancer cells, from cells in the tumour microenvironment or from other cells in the body in response to the presence of the tumour.49 Importantly, exosomes derive from intracellular endosomal compartments50 and some receptor-beta-arrestin-1 complexes co-localise in endosomes,51 thus supporting the fact that beta-arrestin-1 may be part of the exosomal proteome. Here, ARRB1 is linked to cancer.