Altered CRLF2 (cytokine receptor like factor 2) gene expression in B-ALL, especially CRLF2 overexpression, can be caused by deletion of PAR1, by translocations involving immunoglobulin heavy chain genes, e.g. IGH@-CRLF2 and/ or CRLF2 mutations (16). Here, CRLF2 is linked to precursor B-cell acute lymphoblastic leukemia.