a, Exosomal ITGβ4 levels in breast cancer patients who were metastasis-free at the time of blood draw. Amount of ITGβ4 per microgram of exosome in healthy control (Ctrl) subjects (n = 6); patients with ductal carcinoma in situ (DCIS) (n = 7), invasive breast cancer without relapse within three years (NED, no evidence of disease) (n = 8), locoregional recurrence (LR) within three years (n = 2), bone metastasis within three years (n = 3), or lung metastasis within three years (n = 2). POD, progression of disease. b, Exosomal ITGαv in pancreatic cancer patients who were metastasis-free at the time of blood draw. Amount of ITGαv per microgram of exosome in healthy control subjects (n = 13); patients with pancreatic cancer without relapse within three years (n = 14), or liver metastasis within three years (n = 13). c, Model of exosome-mediated organotropic tumour dissemination. Tumour-derived exosomes are uptaken by organ-specific resident cells in future metastatic organs based on integrin expression. Data are mean ± s.e.m. * P < 0.05; ** P < 0.01 by one-way ANOVA.