ARRB1 and cancer: Nevertheless, beta-arrestin-1 protein was previously identified in extracellular vesicles derived from various cancer cell lines45 and from primary monocyte-derived dendritic cells.46 Additionally, beta-arrestin-1 was detected in extracellular vesicles isolated from human milk47 and urine.48 These data suggest that beta-arrestin-1 may be shed by the cells and released into biofluids (in this case, plasma) via exosomes, microvesicles or other extracellular vesicles.