Inhibition of platelet function: does it offer a chance of better cancer progression control?

Thrombocytosis is frequently (10 to 57%) observed in cancer patients. Although the mechanisms underlying thrombocytosis are not yet fully elucidated, tumor-derived factors with thrombopoietin-like activity, growth factors, platelet-derived microparticles, and factors released from bone marrow endothelial cells as well as growth factors secreted by megakaryocytes (acting via an autocrine loop) are claimed to influence this process. The course of cancer is strongly associated with hypercoagulable state, which results from direct influences of tumor cells themselves and various indirect mechanisms. Activated platelets provide procoagulant surface amplifying the coagulation process. It is well documented that proteins of the hemostatic system influence different steps of metastasis, angiogenesis, and proteolytic events. Much less is known about the role of platelets in tumor growth and their possible contribution to prevention of tumor cells from the host immune system. Multidirectional activities of platelets during tumor development and metastatic dissemination create a possibility of introducing antiplatelet agents in anticancer therapy. The spectrum of plausible therapies includes antibodies against glycoprotein IIb-IIIa, direct thrombin inhibitors, protease activated receptor-1 targeted therapy, as well as cyclooxygenase (COX) and lipoxygenase (LOX) inhibitors. However, there is no sufficient information on a specific type of cancer where progression does depend on platelet function. Despite numerous experimental studies conducted, to date none of the new specific antiplatelet agents were tested in clinical trials in a cancer patient population.