For immunohistochemical analysis, the PET/CT imaging and biodistribution cohort (n=6) tumors were used. Tumor ipsilateral right brain and contralateral left-brain samples were fixed in neutral phosphate-buffered 10% formalin (Fisher Scientific, Pittsburgh, PA) for 24 h. Samples were then transferred to 70% ethanol until the Zr-89 decayed (>5 half-lives). Samples were dehydrated using an EtOH gradient of 70% to 100% over 24 h, cleared with histology grade xylene (Fisher Scientific), embedded in granular paraffin, and sectioned (5 μm) on poly-lysine slides. Sections were incubated with 10% normal goat serum, and then overnight at 4°C with primary antibody. Biotinylated secondary goat anti-rabbit Ab (Abcam; dilution 1:200) was used to detect the primary Ab. The staining signal was amplified with avidin-biotin complex (Vector Laboratories, Burlingame, CA) and developed using chromogen 3-amino-9-ethylcarbazole (Sigma-Aldrich). ImageJ software (ImmunoRatio plugin) was used to quantify CD11b+ cells per nuclear area [20 (link)]. A histomorphologic analysis of the tumors was performed with the H&E slides.