While the FLT3/ITD mutation alone induces a lethal myeloproliferative neoplasm (MPN) [7] and the Nup98-HoxD13 translocation alone produces a myelodysplastic syndrome (MDS), mice bred to express both mutations develop an acute leukemia with short latency and 100% penetrance. This evidence concerns the gene HOXD13 and myeloproliferative neoplasm.