It has to be noted that the Kyn/Trp ratio is not fully reflecting IDO1 activity in vivo,10 but there is evidence for the prognostic value of the Kyn/Trp ratio in glioblastoma, nasopharyngeal carcinoma and non‐small cell lung cancer patients.36, 37, 38. The gene discussed is IDO1; the disease is nasopharyngeal carcinoma.