FLT3 and myeloproliferative disorder: FLT3 ITD promotes factor-independent growth and blocks the differentiation of myeloblastic cells in vitro (9, 10, 20). Moreover, it has been shown to induce leukemic cell transformation in vitro (10) and to drive the developmentof myeloproliferative disease in murine bone marrow transplantation models (14, 21).