Huang JY, et al. - Given a possible significant role of cell-mediated immune suppression in lung carcinogenesis, researchers examined 5,364 smoking-matched case-control pairs from 20 prospective cohorts included in the international Lung Cancer Cohort Consortium, for the associations for circulating levels of tryptophan, kynurenine, kynurenine:tryptophan ratio (KTR), quinolinic acid (QA), and neopterin as markers of immune regulation and inflammation with lung cancer risk. Serum/plasma samples collected on average 6 years before lung cancer diagnosis were examined for all biomarkers using mass spectrometry-based methods. Outcomes revealed an association between components of the tryptophan-kynurenine pathway with immunomodulatory effects and the risk of lung cancer overall. This association was particularly evident among current smokers.