Overexpression of thioredoxin system proteins predicts poor prognosis in patients with squamous cell carcinoma of the tongue.

The human thioredoxin (Trx) system plays a critical role in the regulation of cellular reduction-oxidation (redox) homeostasis, which has been widely investigated in several types of cancer because of its association with cell growth and anti-apoptosis progress. This study aimed to evaluate the expression of Trx and Trx reductase-1 (TrxR-1) and explore the potential role of these proteins in tongue squamous cell carcinoma (TSCC). Immunohistochemistry was employed to analyze the protein expression levels of Trx and TrxR-1 in 65 TSCC tissue samples and 10 normal oral mucosa samples. The results were then evaluated semiquantitatively and compared to other clinicopathological variables. Both Trx and TrxR-1 expression levels were significantly higher in TSCC tissues as compared with the 10 normal oral mucous samples (P<0.01). A highly significant association between Trx and TrxR-1 expression in TSCCs was revealed (P=0.001), and the expression of Trx was correlated with tumour cell differentiation (P=0.001). Moreover, Kaplan-Meier analysis revealed that Trx expression and TNM stage were significantly related with 5-year survival rate (P=0.033, 0.000), while TrxR-1 expression was not associated with survival (P=0.092). The results indicated that high expression of Trx and TrxR-1 was associated with tumourigenesis in TSCC, and overexpression of Trx might predict poor prognosis.