We performed liquid chromatography‐tandem mass spectrometry (LC‐MS/MS) to detect Trp metabolism in tumor cells, and found I3A treatment induced Trp and Phe accumulation besides I3A in tumor cells (Figure 3B), potentially as a result of a negative feedback loop on Trp metabolism mediated by IL4I1. The gene discussed is IL4I1; the disease is neoplasm.