Identification of the platelet- and plasma-derived candidate proteins. Platelets were harvested from mice bearing nonangiogenic or angiogenic xenografts of human liposarcoma at 30 days after tumor implantation and compared with those of their littermate controls using a standard SELDI-ToF biomarker discovery method. A spectral readout from SELDI-ToF MS is presented here in gel view format, and groups are color-coded for clarity. Gray represents protein content of platelets from control animals; blue, from mice bearing the nonangiogenic dormant clone; and red, from mice bearing the angiogenic clone. A differentially expressed protein was observed at 8206 Da. The candidate peptide (↑) was later analyzed and identified as PF-4. Each horizontal strip represents an individual mouse sample (n = 5), and the color intensity corresponds to the height of the protein peak. The experiment was reproduced on 2 independent occasions for a total of 15 mice per group.