Expression of Indoleamine 2,3-Dioxygenase and Correlation With Pathological Malignancy in Gliomas

BACKGROUND: Indoleamine 2,3-dioxygenase (IDO) is a tryptophan catabolic enzyme involved in immune tolerance and tumor immune escape processes. Recently, IDO expression has been found to correlate with the prognosis of malignant tumors, but the implication of IDO in glioma progression remains unknown. OBJECTIVE: To investigate the relationship between IDO expression and histological malignancy in gliomas. METHODS: IDO expression was examined in a total of 75 surgical specimens obtained from 68 patients with glioma using immunohistochemical staining. The 75 specimens included 15 diffuse astrocytomas, 21 anaplastic astrocytomas, and 39 glioblastomas. Six of 39 glioblastomas were secondary glioblastomas, transforming from grade II or III gliomas that had been determined at the first surgery. IDO expression rate was compared in each histological grade, and patient survival was analyzed. RESULTS: Expression of IDO was found in 72 of 75 gliomas at varying intensities. Stronger expression of IDO was more likely to be observed in malignant gliomas compared with low-grade gliomas. IDO expression in the 6 cases of secondary glioblastoma was stronger than in the initial low-grade glioma. Survival analysis using the Kaplan-Meier method revealed that grade IV patients with strong IDO expression had significantly worse overall survival rates (P =.04) than patients with weak IDO expression. CONCLUSION: IDO is expressed more strongly in both primary and secondary glioblastoma tissue than low-grade glioma and may affect clinical outcome. If IDO promotes glioma cells to escape from the immune system, IDO may be a crucial therapeutic target for malignant gliomas.