PF-4/CXCL4 is a member of the CXC chemokine family produced by cells of the megakaryocytic lineage. In megakaryocytes CXCL4 is synthesized, enclosed in vesicles, and transferred to the granules from which it is secreted following platelet activation.1 More recently, CXCL4 expression was also found in monocytes. The first biological function described for CXCL4 is its antiheparin activity, responsible for the important role of CXCL4 in the regulation of coagulation processes.Chemokines regulate leukocyte migration during physiological and pathological conditions. It is currently accepted that these chemotactic cytokines are also important in the development and progression of cancer. CXCL4 and its non-allelic variant CXCL4L1 are two platelet-associated chemokines that have been attributed anti-tumoral activity as a result of their angiostatic potential and the chemotactic activity for anti-tumoral leukocytes.