Abstract
PURPOSE: Tryptophan metabolites have immunomodulatory functions, suggesting possible roles in cancer immunity. METHODS: Plasma tryptophan metabolites were measured using liquid chromatography/mass spectrometry before immune checkpoint inhibitors (ICIs) in patients with non-small cell lung cancer (NSCLC). RESULTS: The 19 patients with NSCLC had significantly lower levels of tryptophan (p = 0.002) and xanthurenic acid (p = 0.032), and a significantly higher level of 3-hydroxyanthranilic acid (3-HAA) (p = 0.028) compared with the 10 healthy volunteers. The patients achieving objective responses had significantly lower levels of 3-HAA than those who did not (p = 0.045). Receiver operating characteristic analyses determined that the cutoff value of 3-HAA for objective response was 35.4 pmol/mL (sensitivity: 87.5% and specificity: 83.3%). The patients with 3-HAA < 35.4 pmol/mL had significantly longer median progression-free survival (7.0 months) than those without (1.6 months, p = 0.022). CONCLUSIONS: Tryptophan metabolites may have a potential for predicting the efficacy of ICIs. REGISTRATION NUMBER: University Hospital Medical Information Network Clinical Trial Registry 000026140.