Unique gene expression profiles were later found to be associated with leukemic arrest of thymocytes at different developmental stages [15], leading to the definition of new T-ALL subgroups characterized by the driver oncogenes or oncogene fusions (TAL/LMO, TLX1, TLX3, HOXA, and MYB genes), denoted as type A aberrations, present at diagnosis [16]. The gene discussed is TLX1; the disease is acute lymphoblastic leukemia.