Genome-wide gene expression studies have led to the definition of molecular subgroups of T-ALL, characterized by the ectopic expression of particular proto-oncogenes (e.g., TAL1, LMO1, LMO2, TLX1, TLX3, and HOXA) and associated different disease prognosis (extensively reviewed by van Vlierbergh et al. [49]). The gene discussed is TAL1; the disease is acute lymphoblastic leukemia.