Pham QT, et al. - Researchers analyzed the expression and biological significance of tryptophan 2,3-dioxygenase (TDO2), an enzyme involved in tryptophan catabolism, in esophageal squamous cell carcinoma (ESCC). They found that, TDO2 overexpression was related to tumor stage, recurrence status, and the CD44 cancer stem cell marker in ESCC. In ESCC patients, correlation with poor outcome was demonstrated by TDO2 overexpression. Both the number and the size of spheroid colonies as well as cell proliferation were attenuated by inhibition of TDO2 expression by RNA interference (RNAi) in TE-10 and TE-11 cell lines. Overall, in ESCC, a possible important role of TDO2 in the disease progression as well as possible value as a potential therapeutic target was suggested.