Illegitimate RAG-mediated recombination has been proposed to be involved in the translocation process of the LMO2 and TAL1 proto-oncogenes with TCRδ[18], and appears to be the cause of recurrent intragenic deletions of the IKZF1 gene in BCP-ALL and lymphoid blast crisis in chronic myeloid leukemia (CML) [19], [20]. The gene discussed is IKZF1; the disease is chronic myelogenous leukemia, BCR-ABL1 positive.