CSF1R signaling regulates tumor recruitment of myeloid cells from peripheral blood. 3LL tumor-bearing mice (day 10 after implantation) were treated with control diluent or GW2580 (for 4 hours) and subsequently intravenously injected with 20 × 10⁶ CFSE-labeled BMCs. After 4 hours, animals were killed and tissues were analyzed for recruitment of CSFE⁺ BMCs by flow cytometry. (A-B) Percentage of CFSE⁺ BMCs in tumor and absolute number of cells/mg tumor are shown (n = 4/group). (C) The majority of tumor-recruited CFSE⁺ cells were CD11b⁺Gr-1⁺ and Ly6C^hi. (D-F) Percentage of CFSE⁺ BMCs in the bone marrow, peripheral blood, and spleens are shown (n = 4/group).