Mechanistically, Phd2 deficiency (i) increased the number of tumor-associated macrophages in AOM/DSS-induced tumors, (ii) promoted the expression of EGFR ligand epiregulin in macrophages, and (iii) augmented the signal transducer and activator of transcription 3 and extracellular signal–regulated kinase 1/2 signaling, which at least in part contributed to aggravated tumor cell proliferation in colitis-associated tumors. The gene discussed is STAT3; the disease is colitis.