IDO1 and cancer: In addition to anti-cancer effects, EGCG shows a significant inhibitory effect on interferon-γ (IFN-γ)-induced indoleamine 2,3-dioxygenase (IDO) expression, an enzyme that guides cancer to regulate immune response, in human colorectal cancer SW-837 cells [108], so this suggests that EGCG might be useful for chemoprevention and colorectal cancer treatment, and could be a potential agent for anti-tumor immunotherapy.