LC growth factors were not expressed at high levels by in vivo tumors; however, we observed significant increases in Pros1 and Gas6; both TAM receptor ligands have previously been associated with the suppression of anti-tumor immunity (73, 74), and Pros1 is known to inhibit differentiation of bone marrow–derived LCs (75), suggesting that growing melanomas may directly impair LC function in situ before migration. Here, GAS6 is linked to melanoma.