The association between IDO activity and clinical prognosis in patients with early stage non-small cell lung cancer after stereotactic body radiotherapy.

Abstract

e21054 Background: Immunity affects the efficacy of radiotherapy of lung cancer patients. Indoleamine 2,3-dioxygenase (IDO) is a key enzyme that converts tryptophan (T) into heparin (K), which can promote immune suppression and assist tumor cells in immune evasion. The purpose of this study was to quantitatively analyze the immune activity of IDO in serum before and after SBRT, and to explore the changes in immune activity of IDO mediated by SBRT and its relationship with patient's survival. Methods: High-performance liquid chromatography and mass spectrometry were used to determine serum K and T in 30 patients with early non-small cell lung cancer before and after SBRT treatment. K: T stands for IDO activity. The Kaplan-Meier method and log-rank test were used to evaluate the correlation between overall survival (OS), progression-free survival (PFS), and IDO activity. Cox proportional hazards model was used for univariate and multivariate analyses. Results: The median follow-up time was 37.4 months. The median PFS was 37.5 (95% CI, 31.0-44.0) months. The median survival was not reached. In all patients, lower post/pre kynurenine ratio correlated significantly with better PFS (HR = 0.31, 95% CI = 0.11-0.90, P = 0.032). The lower K: T ratio at post-RT received longer OS (HR = 0.27, 95% CI = 0.079-0.95, P = 0.042). In multivariate analysis, smoking < 30 packs / year (P = 0.030), higher BED (P < 0.001), and lower post/pre kynurenine (P = 0.043) were associated with better PFS. Lower K: T ratio post-RT (P = 0.040) and higher BED (P < 0.001) were significantly associated with better OS. Conclusions: SBRT could alter IDO-mediated antitumor immune activity. The lower level of post/pre kynurenine ratio was significantly related with better PFS. The lower K: T ratio at post-RT was related with better OS. This study shows that IDO is a potentially valuable biomarker for monitoring the immune status and predicting survival in early NSCLC patients after SBRT.