ARG1 and colon carcinoma: As shown in Figure 1A, we confirmed that the expression of Arg-1, a key marker of macrophage M2 polarization, is induced in Raw264.7 macrophage cells treated with conditioned culture media obtained from 3 different tumor cell types, including CT26 colon carcinoma cells, Lewis lung carcinoma LLC cells, and B16-F10 melanoma cells.