TLX1 and acute lymphoblastic leukemia: The TLX1/NKX2.1 (T-cell leukemia homeobox protein 1/NK2 homeobox 1) subtype presents in 10% T-ALL with genomic rearrangements involving either TLX1 or NKX2.1, CD1 expression, and differentiation arrest at the cortical stage; it is a proliferative subtype, and it correlates with excellent outcome in patients.