Deregulation of the intracellular Ras signal transduction pathway, which is induced in >90% of patients by mutations in one (or, rarely, more than one) of five primordial genes (PTPN11, NRAS, KRAS, NF1, or CBL), is the shared molecular characteristic of JMML [22]. Here, KRAS is linked to juvenile myelomonocytic leukemia.