Conditional Kras G12D expression in hematopoietic stem cell (HSC), under the control of Mx1-Cre, lead to myeloproliferative disease (MPD) reminiscent of chronic myelomonocytic leukemia (CMML) or juvenile myelomonocytic leukemia (JMML) in all mice, and to concomitant T cell leukemia in a small fraction of mice. Here, KRAS is linked to juvenile myelomonocytic leukemia.