Differently from BCP-ALL, the molecular mechanisms responsible for CRLF2 over-expression in T-ALL remains to be determined, since none of the tested CRLF2-high cases resulted to be positive for P2RY8-CRLF2 fusion or IGH@-CRLF2 translocation, and only one showed a supernumerary X chromosome. The gene discussed is CRLF2; the disease is acute lymphoblastic leukemia.