PF-4 in platelets of mice bearing human-tumor xenografts. Platelets of mice bearing xenografts of SW872 liposarcoma (A), MDA-MB-436 mammary adenocarcinoma (B), or KHOS-24 osteosarcoma (C) were analyzed using SELDI-ToF. The blue bars represent whole platelet extracts and brown bars represent plasma. The platelets of non–tumor-bearing control mice served as a reference for the endogenous levels of platelet- and plasma-derived PF-4. The control group is shared by all 3 experiments. Platelets of nonangiogenic or angiogenic human liposarcoma xenografts, SW872, exhibited a 7-fold elevation of platelet-derived PF-4 compared with non–tumor-bearing controls at 30 days after implantation (A) without a corresponding increase of PF-4 in the plasma. Platelets of mice bearing the angiogenic mammary adenocarcinoma, MDA-MB-436 (B), also had significant elevation of platelet but not plasma PF-4. In the case of angiogenic osteosarcoma, KHOS-24OS (C), a similar trend at 4- and 2-fold up-regulation can be observed, but the value did not reach significance. Each bar represents the mean peak intensities corresponding to the level of the protein (± SEM) of 5 to 10 mice per experiment. Student t test was used to compare means of the groups. Each experiment was repeated twice.