Indoleamine 2,3-dioxygenase 1 and overall survival of patients diagnosed with esophageal cancer.

Background: Indoleamine 2,3-dioxygenase 1 (IDO1) is an enzyme with immunomodulatory properties that has emerged as a potential immunotherapeutic target in human cancer. However, the role, expression pattern, and relevance of IDO1 in esophageal cancer (EC) are poorly understood. Here, we utilize gene expression analysis of the cancer genome atlas (TCGA) and immunohistochemistry (IHC) to better understand the role and prognostic significance of IDO1 in EC.

Results: High IDO1 mRNA levels were associated with worse overall survival (OS) in both esophageal squamous cell carcinoma (SCC) ( P = 0.02) and adenocarcinoma (AC) ( P = 0.036). High co-expression of IDO1 and programmed death ligand 1 (PD-L1) was associated with worse OS in SCC ( P = 0.0031) and AC ( P = 0.0186). IHC for IDO1 in SCC showed a significant correlation with PD-L1 ( P < 0.0001) and CD3ε ( P < 0.0001).

Conclusions: EC with high IDO1 and PD-L1 expression is significantly correlated with decreased patient survival, and may correlate with increased T-cells. These data suggest that simultaneous inhibition of IDO1 and PD-(L)1 may overcome important barriers to T-cell mediated immune rejection of EC.

Materials and Methods: mRNA expression data from TCGA (SCC N = 87; AC N = 97). IHC in a second cohort of EC ( N = 93) were stained for IDO1, PD-L1, and CD3ε, followed by light microscopic analysis.