Juvenile Myelomonocytic Leukemia

Juvenile myelomonocytic leukemia (JMML), formerly termed juvenile chronic myeloid leukemia, is a rare hematopoietic malignancy of childhood accounting for less than 1% of all childhood leukemias.[1] A number of clinical and laboratory features distinguish JMML from adult-type chronic myeloid leukemia. The diagnostic criteria that need to be met for JMML are included in Table 4.[2,3]

Table 4. Diagnostic Criteria for Juvenile Myelomonocytic Leukemia (JMML)

The pathogenesis of JMML has been closely linked to activation of the RAS oncogene pathway, along with related syndromes.[3] In addition, distinctive RNA expression and DNA methylation patterns have been reported.[4,5]

Children with neurofibromatosis 1 (NF1) and Noonan syndrome are at increased risk for developing JMML,[6,7] and up to 14% of cases of JMML occur in children with NF1.[8] Approximately 75% of JMML cases harbor one of three mutually exclusive mutations leading to activated RAS signaling, including direct oncogenic RAS mutations (approximately 20%),[9,10] NF1 inactivating mutations (approximately 15%–25%),[11] or protein tyrosine phosphatase, non-receptor type 11 (PTPN11) (SHP-2) mutations (approximately 35%).[12,13] Mutations of the E3 ubiquitin ligase CBL are observed in 10% to 15% of JMML cases,[14,15] with many of these cases occurring in children with germline CBL mutations.[16,17]CBL germline mutations result in an autosomal dominant developmental disorder that is characterized by impaired growth, developmental delay, cryptorchidism, and a predisposition to JMML.[16] Some individuals with CBL germline mutations experience spontaneous regression of their JMML, but develop vasculitis later in life.[16]CBL mutations are mutually exclusive with RAS/PTPN11 mutations.[14] Noonan syndrome, which is usually inherited as an autosomal dominant condition, but can also arise spontaneously, is characterized by facial dysmorphism, short stature, webbed neck, neurocognitive abnormalities, and cardiac abnormalities. Importantly, some children with Noonan syndrome have a hematologic picture indistinguishable from JMML that self-resolves during infancy, similar to what happens in children with Down syndrome and transient myeloproliferative disorder.[3]

Historically, more than 90% of patients with JMML died despite the use of chemotherapy,[18] but with the application of hematopoietic stem cell transplant (HSCT), survival rates of approximately 50% are now reported.[19] Patients appeared to follow three distinct clinical courses: (1) rapidly progressive disease and early demise; (2) transiently stable disease followed by progression and death; and (3) clinical improvement that lasted up to 9 years before progression or, rarely, long-term survival. Favorable prognostic factors for survival after any therapy include being younger than 3 years, having a platelet count of greater than 33 × 10⁹ /L, and low age-adjusted fetal hemoglobin levels.[8,20] In contrast, being older than 3 years and having high blood fetal hemoglobin levels at diagnosis are predictors of poor outcome.[8,20] It remains controversial whether specific mutations are predictive of outcome.[21]

The role of conventional antileukemia therapy in the treatment of JMML is not defined. The absence of consensus response criteria for JMML complicates determination of the role of specific agents in the treatment of JMML.[22] Some of the agents that have shown antileukemia activity against JMML include etoposide, cytarabine, thiopurines (thioguanine and 6-mercaptopurine), and isotretinoin, but none of these have been shown to improve outcome.[21,22,23,24,25]

HSCT offers the best chance of cure for JMML.[19,26,27,28] A report from the European Working Group on Childhood myelodysplastic syndrome notes a 55% and 49% 5-year event-free survival for a large group of children with JMML transplanted with HLA-identical matched family donors or unrelated donors, respectively.[19] The trial included 100 recipients at multiple centers using a common preparative regimen of busulfan, cyclophosphamide, and melphalan, with or without antithymocyte globulin. Recipients had been treated with varying degrees of pretransplant chemotherapy or differentiating agents and some patients had splenectomy performed. Multivariate analysis showed no effect on survival of prior AML-like chemotherapy versus low-dose chemotherapy or none; no effect on survival was observed for the presence or absence of a spleen, difference in spleen size, or related versus unrelated donors. Only gender and age older than 4 years were shown to be poor prognostic factors for outcome (relative risk [RR] 2.24 [1.07–4.69], P = .032, RR 2.22 [1.09–4.50], P = .028 for older age and female gender, respectively). The use of reduced-intensity preparative regimens in order to reduce the adverse side effects of transplantation have also been reported in small numbers of patients, with variable success.[29,30]

Disease recurrence is the primary cause of treatment failure for children with JMML following HSCT and occurs in 30% to 40% of cases.[19,26,27] While the role of donor lymphocyte infusions is uncertain,[31] it has been reported that approximately 50% of patients with relapsed JMML can be successfully treated with a second HSCT.[32]

Current Clinical Trials

Check for U.S. clinical trials from NCI's list of cancer clinical trials that are now accepting patients with juvenile myelomonocytic leukemia. The list of clinical trials can be further narrowed by location, drug, intervention, and other criteria.

General information about clinical trials is also available from the NCI Web site.

References:

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