Platelets favor the outgrowth of established metastases

Despite abundant evidence demonstrating that platelets foster metastasis, anti- platelet agents have low therapeutic potential due to the risk of hemorrhages. In addition, whether platelets can regulate metastasis at the late stages of the disease remains unknown. In this study, we subjected syngeneic models of metastasis to various thrombocytopenic regimes to show that platelets provide a biphasic contribution to metastasis. While potent intravascular binding of platelets to tumor cells efficiently promotes metastasis, platelets further support the outgrowth of established metastases via immune suppression. Genetic depletion and pharmacological targeting of the platelet-specific receptor GPVI in humanized mouse models efficiently reduced the growth of established metastases, independently of active platelet binding to tumor cells in the bloodstream. Our study is the first to demonstrate therapeutic efficacy when targeting animals bearing growing metastases. It further identifies GPVI as the first molecular target whose inhibition can impair metastasis without inducing collateral hemostatic perturbations.