Myelodysplastic Syndromes

The myelodysplastic (MDS) and myeloproliferative (MPS) syndromes, which represent between 5% and 10% of all myeloid malignancies in children, are a heterogeneous group of disorders with the former usually presenting with cytopenias and the latter with increased peripheral white blood cell (WBC), red blood cell, or platelet counts. MDS is characterized by ineffective hematopoiesis and increased cell death, while MPS is associated with increased progenitor proliferation and survival. Because they both represent disorders of very primitive, multipotential hematopoietic stem cells, curative therapeutic approaches nearly always require allogeneic stem cell transplantation.

Patients usually present with signs of cytopenias, including pallor, infection, or bruising. The bone marrow is usually characterized by hypercellularity and dysplastic changes in myeloid precursors. Clonal evolution eventually can lead to the development of acute myeloid leukemia (AML). The percentage of abnormal blasts is less than 20%. The less common, hypocellular MDS, can be distinguished from aplastic anemia in part by its marked dysplasia, clonal nature, and higher percentage of CD34-positive precursors.[1,2]

Although the etiology of MDS has not been elucidated, clues have begun to be defined. For instance, approximately 20% of malignant myeloid disorders, including MDS, in adults have been shown to have mutations in the TET2 gene.[3] Other genes shown to be mutated in MDS include EZH2, DNMT3A, ASXL1, IDH1/2, RUNX1, ETV6/TEL, and TP53. Most of these genes are key elements of epigenetic regulation of the genome and affect DNA methylation and/or histone modification.[3,4,5] Mutations in proteins involved in RNA splicing have been described in 45% to 85% of MDS.[6] MDS in both adults and children has been shown to have aberrant DNA methylation patterns and approximately one-half of cases are characterized by hypermethylation of the promoters for the CDKN2B and CALC genes, both of which play roles in cell cycle regulation.[7,8] Inherited disorders, such as Fanconi anemia, due to germline mutations in DNA repair genes, or in dyskeratosis congenita, due to mutations in genes regulating telomere length, have significantly increased risk of developing MDS.[9] Additional bone marrow failure syndromes may also evolve into MDS, including those due to mutations in genes encoding ribosome associated proteins, such as Shwachman-Diamond syndrome and Diamond-Blackfan anemia.[9] The 15-year cumulative risk of MDS in patients with severe congenital neutropenia, also know as Kostmann syndrome, which is due to mutations in the gene encoding elastase, has been estimated to be 15% with an annual risk of MDS/AML of 2% to 3%; how mutations affecting this protein as well as what role the chronic exposure of granulocyte-colony stimulating factor (G-CSF) contribute to the development of MDS is unclear.[10,11] Inherited mutations in the RUNX1 or CEPBA genes have also been shown to be associated with familial MDS/AML.[12,13]

The French-American-British (FAB) and World Health Organization (WHO) classification systems of MDS and MPS have been difficult to apply to pediatric patients. Alternative classification systems for children have been proposed, but none have been uniformly adopted, with the exception of the modified WHO system.[14,15,16,17,18] The WHO system [19] has been modified for pediatrics.[17]

Diagnostic Categories for Myelodysplastic and Myeloproliferative Disease in Children

• Down syndrome (DS) disease
  • Transient myeloproliferative disorder.
  • Myeloid leukemia of DS.
• Myelodysplastic/myeloproliferative disease
  • Juvenile myelomonocytic leukemia (JMML).
• Myelodysplastic syndrome
  • Refractory cytopenia ([RC], previously called refractory anemia [RA])—peripheral blood blasts <2% and bone marrow blasts <5%.
  • Refractory anemia with excess blasts (RAEB)—peripheral blood blasts 2% to 19% or bone marrow blasts 5% to 19%.
  • Refractory anemia with excess blasts in transformation (RAEB-T)—peripheral blood or bone marrow blasts 20% to 29%. In the FAB classification, RAEB-T required evidence of dysplasia, particularly in the red blood cell lineage, and 21% to 30% myeloblasts in the bone marrow; if there was greater than 30% myeloblasts this was considered to be acute myeloid leukemia. In part because of the artificial designation of the percentage of blasts, the WHO classification system now simply considers these patients to have AML and the RAEB-T subtype has been eliminated.

The refractory cytopenia subtype represents approximately 50% of all childhood cases of MDS. The presence of an isolated monosomy 7 is the most common cytogenetic abnormality, although it does not appear to portend a poor prognosis compared with its presence in overt AML. However, the presence of monosomy 7 in combination with other cytogenetic abnormalities is associated with a poor prognosis.[20,21] The relatively common abnormalities of -Y, 20q- and 5q- in adults with MDS are rare in childhood MDS. The presence of cytogenetic abnormalities found in AML defines disease that should be treated as AML and not MDS.[22] The International Prognostic Scoring System (IPSS) can help to distinguish low-risk from high-risk MDS, although its utility in children with MDS is more limited than in adults, in part because children often have more high-risk characteristics compared with adults, especially in terms of cytopenias.[22,23] Nevertheless, the median survival for children with high-risk MDS remains substantially better than adults.[24]

The optimal therapy for childhood MDS has not been established. A key issue in thinking about therapy for pediatric patients with MDS is that these disorders usually involve a primitive hematopoietic stem cell. Thus, allogeneic hematopoietic stem cell transplantation (HSCT) is considered to be the optimal approach to treatment for pediatric patients with advanced MDS. Unresolved issues include determining the best transplant preparative regimen and source of donor cells.[25,26] However, some data are important to consider when making decisions. For example, disease-free survival has been estimated to be between 50% to 70% for pediatric patients with advanced MDS using myeloablative transplant preparative regimens.[27,28,29,30] While using nonmyeloablative preparative transplant regimens are being tested in patients with MDS and AML, such regimens are still investigational for children with these disorders, but may be reasonable in the setting of a clinical trial or when a patient's organ function is compromised in such a way that they would not tolerate a myeloablative regimen.[31,32,33]

The question of whether chemotherapy should be used in high-risk MDS has been examined. The Children's Cancer Group 2891 trial accrued patients between 1989 and 1995, including children with MDS.[27] There were 77 patients with RA (n = 2), RAEB (n = 33), RAEB-T (n = 26), or AML with antecedent MDS (n = 16) who were enrolled and randomly assigned to standard or intensively timed induction. Subsequently, patients were allocated to allogeneic HSCT if there was a suitable family donor, or randomly assigned to autologous HSCT or chemotherapy. Patients with RA/RAEB had a poor remission rate (45%), and those with RAEB-T (69%) or AML with history of MDS (81%) had similar remission rates compared with de novo AML (77%). Six-year survival was poor for those with RA/RAEB (28%) and RAEB-T (30%). Patients with AML and antecedent MDS had a similar outcome to those with de novo AML (50% survival compared with 45%). Allogeneic HSCT appeared to improve survival at a marginal level of significance (P = .08). Based on analysis of these data and the literature, the authors concluded that children with a history of MDS who present with AML and many of those with RAEB-T do as well with AML therapy at diagnosis as children with AML. An exception to this conclusion is children with AML with a precedent MDS and monosomy 7; these patients have a very poor prognosis and are usually treated with some type of allogeneic HSCT. An analysis of 37 children with MDS treated on Berlin-Frankfurt-Munster AML protocols 83, 87, and 93 confirmed the induction response of 74% for patients with RAEB-T and suggested that transplantation was beneficial.[34] For patients who achieve remission and for whom there is no matched-family donor (MFD), it is unclear whether aggressive continuation of chemotherapy or alternative donor stem cell transplant is optimum therapy.[27]

A significant issue to consider for these results is that the subtype RAEB-T is likely to represent patients with overt AML, while RA and RAEB represent MDS. The optimum therapy for patients with RA/RAEB without MFD is unknown. Some of these patients require no therapy for years and have indolent diseases. Because failure rates after HSCT are lower in this group, strong consideration should be given for such treatment, especially when a 5/6 or 6/6 HLA-MFD is available. However, alternative forms of HSCT, utilizing matched unrelated donor cord blood, should be considered when treatment is required, as is usually the case in patients with severe cytopenias.[28,35]

For patients with clinically significant cytopenias, supportive care, including transfusions and prophylactic antibiotics, can be considered, but have not been proven to be curative; however, it is important that supportive care be utilized in these patients awaiting transplant. In addition, the use of hematopoietic growth factors can improve the hematopoietic status, but there is some concern that such treatment could accelerate conversion to AML.[36] Steroid therapy has also been used, including glucocorticoids and androgens, with mixed results.[37] Treatments directed toward scavenging free oxygen radicals with amifostine [38,39] or the use of differentiation-promoting retinoids,[40] DNA methylation inhibitors, and histone deacetylase inhibitors, have all shown some positive responses. Azacytidine has been FDA-approved for the treatment of MDS in adults based on randomized studies.[41] Agents, such as lenalidomide, an analog of thalidomide, have been tested based on findings that demonstrated increased activity in the bone marrow of patients with MDS. Lenalidomide has shown most efficacy in patients with 5q- syndrome and is now FDA-approved for use in this group.[42] Immunosuppression with antithymocyte globulin and/or cyclosporine has also been reported.[42,43]

Treatment Options Under Clinical Evaluation

The following are examples of national and/or institutional clinical trials that are currently being conducted.

• The use of a variety of inhibitors of DNA methylation and histone deacetylase inhibitors, as well as other therapies designed to induce differentiation, are being studied in both young and older adults with MDS.[44,45,46]

Current Clinical Trials

Check for U.S. clinical trials from NCI's list of cancer clinical trials that are now accepting patients with childhood myelodysplastic syndromes. 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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