Juvenile myelomonocytic leukemia (JMML) is a rare form of chronic leukemia (cancer of the blood) that affects children, commonly those aged four and younger. The name JMML now encompasses all diagnoses formerly referred to as juvenile chronic myeloid leukemia (JCML), chronic myelomonocytic leukemia of infancy, and infantile monosomy 7 syndrome. The average age of patients at diagnosis is two (2) years old. The World Health Organization has included JMML as a subcategory of myelodysplastic and myeloproliferative disorders.

Reference
Wiki: Juvenile myelomonocytic leukemia