Juvenile myelomonocytic leukemia (JMML) is an aggressive childhood myeloproliferative
disorder characterized by the overproduction of myelomonocytic cells. JMML incidence
approaches 1.2/million persons in the United States (Cancer Incidence and Survival Among
Children and Adolescents: United States SEER Program 1975–1995). Although rare, JMML
is innately informative as the molecular genetics of this disease implicates hyperactive Ras
as an essential initiating event. Given that Ras is one of the most frequently mutated …