G-CSF administration increases tumor burden in bone in vivo. A. Mice were administered 200 μg/kg G-CSF (n = 13) or vehicle (n = 12) daily for 8 days. On the fifth day of treatment, 104 B16-FL tumor cells were injected into the right tibia. Tumor burden was assessed by bioluminescence imaging at days 8, 10, and 12 after tumor cell injection. A representative image from day 12 is shown here. G-CSF–administered mice demonstrated an increased tumor burden compared with vehicle-administered animals (P < .006, G-CSF vs vehicle; pooled data from 2 independent experiments; y-axis is log scale). (B) After tumor cells were injected (12 days), mice were killed and bones were isolated. Histomorphometric analysis confirmed the increased tumor burden seen by imaging in the G-CSF–administered animals (P = .01). Representative histology depicted here; M indicates marrow; T, tumor. All error bars represent standard error of the mean. Asterisks indicate statistical significance.
