TET1 was found to act as oncogene in MLL-rearranged leukemia.222TET1 expression was decreased, whereas the expression of TET2 and TET3 was increased in AML.223,224 In refractory AML, TET1 expression was increased compared to that in treatment-responsive patients.225 Moreover, TET1, TET2, and TET3 overexpression was found to be related to poor prognosis in AML.223,224,226 The expression of TET1 and TET3 decreased in CLL, and high TET2 expression was related to longer survival in CLL.227 In addition, TET mutations could also be observed in hematological malignancies. This evidence concerns the gene TET1 and leukemia.