Tumor growth is enhanced in the absence of platelet α-granule–derived TSP-1. Lethally irradiated WT mice were reconstituted with BM from GFP mice. Mice were implanted with B16-F10 tumors and injected with platelets from WT or TSP-1^−/− mice (black columns). Control represents mice bearing tumors without platelet infusion (white columns). (A) After 9 days tumors were excised, weighed, and represented as mean weight ± SEM (n = 10). (B) Whole blood samples were collected from mice after tumor implantation. Red blood cells were lysed, and the sample was labeled with CXCR4 antibody conjugated with phycoerythrin and analyzed by flow cytometry. Levels of CXCR4⁺ cells in the circulation are represented as mean percentage ± SEM (n = 4). *P < .05 vs control or WT (Student t test). **P < .01 vs control or WT (Student t test). ***P < .005 vs control or WT (Student t test).