FOLR2 and neoplasm: A small fraction of peritoneal macrophages, as defined by their CD45, CD11b, and F4/80 expression (Supplementary Fig. 1a), showed positive surface expression of FRβ immediately (12.36 ± 4.51%) or 2 weeks (18.70 ± 3.47%) after tumor inoculation (Fig. 1a).