In addition to IDO catabolizing tryptophan, it has been described that interleukin 4‐induced gene 1 (IL4I1), a secreted enzyme belonging to the L‐amino acid oxidase family, is able to promote the cancer immunosuppressive capacity of aryl‐hydrocarbon receptors (AHRs) more potently than IDO1, previously recognized as the major Trp catabolic enzymes (Sadik et al., 2020). The gene discussed is IDO1; the disease is cancer.