While too extensive to completely review here, different tryptophan-derived ligands such as FICZ [179], 2-(10-H-indole-3-carbonyl) thiazole-4-carboxylic acid methyl ester (ITE) [180], and indole-3-carbinol (I3C) [181] have been explored as experimental and therapeutic AhR agonists [54] for cancer [5,10,182,183,184] and immune diseases [5]. The gene discussed is AHR; the disease is cancer.