Prior to the revision in 2008, JMML was diagnosed based on the following criteria: presence of peripheral blood monocytosis (>1000/μL); less than 20% blasts in the bone marrow; absence of Philadelphia (Ph) chromosome or BCR-ABL fusion gene AND at least two of the following criteria: increased HbF levels; presence of immature myeloid precursors in the peripheral blood; white blood cell count >10,000/μL; GM-CSF hypersensitivity of myeloid progenitors in vitro [5, 9]. Here, CSF2 is linked to juvenile myelomonocytic leukemia.