G-CSF administration does not affect subcutaneous tumor growth. (A) RT-PCR was performed on mRNA harvested from murine tumor cell lines. None of the tumor cell lines express the G-CSF receptor. Spleen cDNA was used as a positive control. (B) Mice were administered 200 μg/kg G-CSF (n = 5 for each cell line) or drug vehicle (n = 5 for each cell line) daily for 8 days. On the fifth day of administration, 5 × 10⁵ B16-FL or 4T1-GFP-FL tumor cells were injected subcutaneously. No significant difference in tumor volume was observed between G-CSF– and vehicle-administered mice 12 days post tumor injection (P = .33, B16-FL; P = .96, 4T1-GFP-FL). All error bars represent standard error of the mean.