Platelet-aggregating activities of metastasizing tumor cells. V. In situ roles of platelets in hematogenous metastases.

Intravenous inoculations of B16 cells having high procoagulant, thrombingenerating, and platelet-aggregating (PA) activities resulted in severe platelet reduction and fibrin-rich thromboembolism in the lungs, whereas those of 3LL cells, whose activities were moderate, caused only moderate changes. MH134 cells with low procoagulant, no thrombin-generating and moderate PA activities induced moderate platelet reduction and the formation of thrombi containing less fibrin. In contrast to the respective high and moderate colonizing abilities of B16 and 3LL cells, MH134 cells failed to form lung colonies in half of the recipients. Thrombocytopenia markedly impaired lung colonization by B16 and 3LL cells. However, thrombin injection enhanced lung colonization by MH134 cells.