Administration of granulocyte macrophage colony stimulating factor (GM-CSF) in combination with thrombopoietin (TPO) to patients who had received chemotherapy for acute myeloid leukemia (AML) has been found to cause bone marrow hypercellularity, marked megakaryocytic hyperplasia, megakaryocytic atypia, and reticulin fibrosis with a rapid resolution of the morphologic abnormalities after discontinuation of TPO. The gene discussed is THPO; the disease is acute myeloid leukemia.