The contribution of platelets to intravascular arrest, extravasation, and outgrowth of disseminated tumor cells.

Platelets are primarily known for their contribution to hemostasis and subsequent wound healing. In addition to these functions, platelets play a role in the process of metastasis. Since the first study that suggested a metastasis-promoting function for platelets was published in 1968, various mechanisms have been proposed to explain how platelets contribute to the metastatic process. These include roles in the intravascular arrest of tumor cells, in tumor cell transendothelial migration, in the degradation of basement membrane barriers, in migration and invasion at the metastatic site, and in the proliferation of disseminated tumor cells. Nevertheless, conflicting observations about the role of platelets in these processes have also been reported. Here, we review the in vivo evidence that supports a role for platelets in metastasis formation, propose several scenarios for the contribution of platelets to tumor cell arrest and transendothelial migration, and discuss the evidence that platelets contribute to metastatic invasion and outgrowth.