LEUKEMIA IS THE TERM USED to describe cancer of the bone marrow. In healthy people, bone marrow fills the bones in the body and produces the number of red blood cells (RBCs), white blood cells (WBCs), and platelets that the body needs. In a child with juvenile myelomonocytic leukemia (JMML), the bone marrow creates millions of abnormal WBCs. As the bone marrow becomes packed with these abnormal cells, they crowd out the healthy cells and symptoms of JMML begin to develop.

JMML is a very rare form of childhood leukemia that is most often diagnosed in the first two years of life. This chapter describes JMML and covers risk factors, signs and symptoms, diagnosis, prognosis, and treatment. It concludes with ways to learn about the newest treatments available for JMML.