How I treat juvenile myelomonocytic leukemia.

Juvenile myelomonocytic leukemia (JMML) is a unique, aggressive hematopoietic disorder of infancy/early childhood caused by excessive proliferation of cells of monocytic and granulocytic lineages. Approximately 90% of patients carry either somatic or germline mutations of PTPN-11, K-RAS, N-RAS, CBL, or NF1 in their leukemic cells. These genetic aberrations are largely mutually exclusive and activate the Ras/mitogen-activated protein kinase pathway. Allogeneic hematopoietic stem cell transplantation (HSCT) remains the therapy of choice for most patients with JMML, curing more than 50% of affected children. We recommend that this option be promptly offered to any child with PTPN-11-, K-RAS-, or NF1-mutated JMML and to the majority of those with N-RAS mutations. Because children with CBL mutations and few of those with N-RAS mutations may have spontaneous resolution of hematologic abnormalities, the decision to proceed to transplantation in these patients must be weighed carefully. Disease recurrence remains the main cause of treatment failure after HSCT. A second allograft is recommended if overt JMML relapse occurs after transplantation. Recently, azacytidine, a hypomethylating agent, was reported to induce hematologic/molecular remissions in some children with JMML, and its role in both reducing leukemia burden before HSCT and in nontransplant settings requires further studies.