Truncation mutations affecting the human G-CSFR intracellular domain have been observed in AML, commencing from position 739 through 819 (5, 8–10), and in other leukemias from 738 through 791 (9, 11–14), with truncations across this range able to mediate leukemic transformation in vitro (10) (Figure 1A). This evidence concerns the gene CSF3R and leukemia.