TAL1 and acute lymphoblastic leukemia: On the basis of gene expression profiling, T-ALL cases can be classified into major subgroups that are indicative of leukemic arrest at specific stages of normal thymocyte development (HOX11+ early cortical thymocytes; LYL1+ early pro-T thymocytes; TAL1+ late cortical thymocytes) and have clinical relevance, because they are associated with a favorable or worse prognosis [60].