IL4 and neoplasm: CircRNAs in tumor cells can regulate macrophage polarization through multiple pathways in the TME (Table 3, Fig. 4): (1) they induce crosstalk between tumor cells and macrophages (Fig. 4A), (2) they promote chemokine secretion from tumor cells (Fig. 4B), (3) tumor cell-derived circRNAs in exosomes enter macrophages to play a regulatory role (Fig. 4C), and (4) they promote tumor-cell expression of cytokines such as IL-4 and PD-L1 (Fig. 4D).