Platelet α-granules are necessary for tumor growth, BMDC recruitment, and angiogenesis. Lethally irradiated WT mice were reconstituted with BM from GFP mice. Mice were implanted with B16-F10 tumors and injected with platelets from WT, integrin Beta 3^−/−, Pearl, or VAMP-8^−/− mice (black columns). Control represents mice bearing tumors without platelet infusion (white column). (A) After 9 days tumors were excised, weighed, and represented as mean weight ± SEM (n = 10). (B) Tumors were sectioned and GFP⁺ BMDCs were quantified in tumor sections. Values are represented as mean number GFP⁺ cells per field ± SEM (n = 5). (C) Tumor sections were stained for laminin to visualize vessel density. Vessels were quantified and represented as mean percentage of area ± SEM (n = 5). *P < .05 vs control or WT (Student t test). **P < .01 vs control or WT (Student t test).