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Incidence and Mortality
The MDS are a collection of myeloid malignancies characterized by one or more peripheral blood cytopenias. MDS are diagnosed in slightly more than 10,000 people in the United States yearly, for an annual age-adjusted incidence rate of approximately 4.4 to 4.6 cases per 100,000 people.[
Prognosis
Prognosis is directly related to the number of bone marrow blast cells, to certain cytogenetic abnormalities, and to the amount of peripheral blood cytopenias. By convention, MDS are reclassified as acute myeloid leukemia (AML) with myelodysplastic features when blood or bone marrow blasts reach or exceed 20%. Many patients succumb to complications of cytopenias before progression to this stage. For more information, see the Pathological and Prognostic Systems for MDS section. The acute leukemic phase is less responsive to chemotherapy than is de novo AML.
Pathology
MDS are characterized by abnormal bone marrow and blood cell morphology. Megaloblastoid erythroid hyperplasia with macrocytic anemia, associated with normal vitamin B12 and folate levels, is frequently observed. Circulating granulocytes are often hypogranular or hypergranular and may display the acquired pseudo-Pelger-Huët abnormality. Early, abnormal myeloid progenitors are identified in the marrow in varying percentages. Abnormally small megakaryocytes (micromegakaryocytes) may be seen in the marrow, and hypogranular or giant platelets may appear in the blood.
Clinical Features
MDS occur predominantly in older patients (usually older than 60 years), with a median age at diagnosis of approximately 70 years,[
Risk Factors
Approximately 90% of MDS cases occur de novo with no identifiable cause. Potential environmental risk factors for developing MDS include exposure to the following:[
References:
Myelodysplastic syndromes (MDS) are classified according to features of cellular morphology, etiology, and clinical presentation. The morphological classification of MDS is largely based on the percent of myeloblasts in the bone marrow and blood, the type and degree of myeloid dysplasia, and the presence of ring sideroblasts.[
Pathological Systems
The World Health Organization (WHO) classification [
FAB (1982) | WHO (2008) |
---|---|
AML = acute myeloid leukemia; FAB = French-American-British classification scheme; MDS = myelodysplastic syndromes; WHO = World Health Organization. | |
Myelodysplastic Syndromes | |
Refractory anemia. | Refractory anemia. |
Refractory cytopenia with multilineage dysplasia. Refractory cytopenia with unilineage dysplasia. | |
Refractory anemia with ring sideroblasts. | Refractory anemia with ring sideroblasts. |
Refractory anemia with excess blasts. | Refractory anemia with excess blasts -1 and -2. |
Myelodysplastic syndrome, unclassifiable. | |
Myelodysplastic syndrome associated with del(5q). | |
Reclassified from MDS to: | |
Refractory anemia with excess blasts in transformation. | Acute myeloid leukemia identified as AML with multilineage dysplasia following a myelodysplastic syndrome. |
Chronic myelomonocytic leukemia. | Myelodysplastic and myeloproliferative diseases. |
MDS cellular types and subtypes in either cellular classification scheme have different degrees of disordered hematopoiesis, frequencies of transformation to acute leukemia, and prognoses.
Refractory anemia (RA)
In patients with RA, the myeloid and megakaryocytic series in the bone marrow appear normal, but megaloblastoid erythroid hyperplasia is present. Dysplasia is usually minimal. Marrow blasts are less than 5%, and no peripheral blasts are present. Macrocytic anemia with reticulocytopenia is present in the blood. Transformation to acute leukemia is rare, and median survival varies from 2 years to 5 years in most series. RA accounts for 20% to 30% of all patients with MDS.
Refractory anemia with ring sideroblasts (RARS)
In patients with RARS, the blood and marrow are identical to those in patients with RA, except that at least 15% of marrow red cell precursors are ring sideroblasts. Approximately 10% to 12% of patients present with this type, and prognosis is identical to that of RA. Approximately 1% to 2% of RARS evolve to acute myeloid leukemia (AML).
Refractory anemia with excess blasts (RAEB)
In patients with RAEB, there is significant evidence of disordered myelopoiesis and megakaryocytopoiesis in addition to abnormal erythropoiesis. Because of differences in prognosis related to progression to a frank AML, this cellular classification is composed of two categories: RAEB-1 and RAEB-2. Combined, the two categories account for approximately 40% of all patients with MDS. RAEB-1 is characterized by 5% to 9% blasts in the bone marrow and less than 5% blasts in the blood. Approximately 25% of cases of RAEB-1 progress to AML. Median survival is approximately 18 months. RAEB-2 is characterized by 10% to 19% blasts in the bone marrow. Approximately 33% of cases of RAEB-2 progress to AML. Median survival for RAEB-2 is approximately 10 months.
Refractory cytopenia with multilineage dysplasia (RCMD)
In patients with RCMD, bicytopenia or pancytopenia is present. In addition, dysplastic changes are present in 10% or more of the cells in two or more myeloid cell lines. There are less than 1% blasts in the blood and less than 5% blasts in the bone marrow. Auer rods are not present. Monocytes in the blood are less than 1 × 109. RCMD accounts for approximately 24% of cases of MDS. The frequency of evolution to acute leukemia is 11%. The overall median survival is 33 months. Refractory cytopenia with multilineage dysplasia and ring sideroblasts (RCMD-RS) represents another category of RCMD. In RCMD-RS, features of RCMD are present, and more than 15% of erythroid precursors in the bone marrow are ring sideroblasts. RCMD-RS accounts for approximately 15% of cases of MDS. Survival in RCMD-RS is similar to that in primary RCMD.
Refractory cytopenia with unilineage dysplasia (RCUD)
In patients with RCUD, a single cytopenia is present, involving either erythrocytes, neutrophils, or platelets. In addition, dysplastic changes are present in 10% or more of the cells in two or more myeloid cell lines. There are less than 1% blasts in the blood and less than 5% blasts in the bone marrow. Auer rods are not present. Monocytes in the blood are less than 1 × 109.
Unclassifiable myelodysplastic syndrome (MDS-U)
The cellular subtype MDS-U lacks findings appropriate for classification as RA, RARS, RCMD, or RAEB. Blasts in the blood and bone marrow are not increased.
Myelodysplastic syndrome associated with an isolated del(5q) chromosome abnormality
This MDS cellular subtype, the 5q- syndrome, is associated with an isolated del(5q) cytogenetic abnormality. Blasts in both blood and bone marrow are less than 5%. This subtype is associated with a long survival. Karyotypic evolution is uncommon. Additional cytogenetic abnormalities may be associated with a more aggressive MDS cellular subtype or may evolve to AML.
Therapy-related myeloid neoplasms
The latest version of the WHO pathological classification system identifies patients with therapy-related MDS or AML and places them in the same category as "therapy-related myeloid neoplasms." This group of disorders evolves in patients who were previously treated with chemotherapy or radiation therapy for other cancers and in whom there is a clinical suspicion that the prior therapy caused the myeloid neoplasm. Classic chemotherapy agents associated with these disorders include alkylating agents, topoisomerase inhibitors, and purine nucleoside analogues.
Chronic myelomonocytic leukemia (CMML)
Although previously classified with the myelodysplastic syndromes, CMML is now assigned to a group of overlap myelodysplastic/myeloproliferative neoplasms. For more information, see Myelodysplastic/ Myeloproliferative Neoplasms Treatment.
Prognostic Scoring Systems
A variety of pathological and risk classification systems have been developed to predict the overall survival of patients with MDS and the evolution from MDS to AML. Major prognostic classification systems include the International Prognostic Scoring System (IPSS), revised as the IPSS-R;[
IPSS
The IPSS incorporates bone marrow blast percentage, number of peripheral blood cytopenias, and cytogenetic risk group.
IPSS-R
Compared with the IPSS, the IPSS-R updates and gives greater weight to cytogenetic abnormalities and severity of cytopenias, while reassigning the weighting for blast percentages.[
WPSS
In contrast to the IPSS and IPSS-R, which should be applied only at the time of diagnosis, the WPSS is dynamic, meaning that patients can be reassigned categories as their disease progresses.
MD Anderson
The MD Anderson Cancer Center has published two prognostic scoring systems, one of which is focused on lower-risk patients.[
References:
Therapies for myelodysplastic syndromes (MDS) are initiated in patients with a shorter predicted survival or in patients with clinically significant cytopenias. The impact of most MDS therapies on survival remains unproven.
Treatment options:
Supportive Care
The mainstay of treatment for MDS has traditionally been supportive care, particularly for patients with symptomatic cytopenias or who are at high risk of infection or bleeding.[
No prospective trials have demonstrated the benefit of prophylactic use of myeloid growth factors in asymptomatic neutropenic MDS patients. Similarly, the use of prophylactic antibiotics in such patients is of uncertain benefit. While appropriate use of antibiotics in febrile patients is standard clinical practice, the benefit of myeloid growth factors in such settings is unknown.
The use of erythropoiesis-stimulating agents (ESAs) may improve anemia. The likelihood of response to exogenous erythropoietin administration depends on the pretreatment serum erythropoietin level and baseline transfusion needs.
A meta-analysis summarized the data on erythropoietin in 205 patients with MDS from 17 studies. Responses were most likely in patients who were anemic but who did not yet require a transfusion, patients who did not have ring sideroblasts, and patients who had a serum erythropoietin level lower than 200 IU/L.[
One decision model found that the likelihood of responding to growth factors was higher in patients with a low serum erythropoietin level (<500 IU/L) and low transfusion needs (<2 units of packed red blood cells every month), but growth factors were rarely effective in patients with a high erythropoietin level and high transfusion needs.[
The availability of the oral iron-chelating agent deferasirox has led to its widespread use in patients with MDS. While some consensus panels advocate prophylactic iron chelation in patients with ongoing transfusion needs and substantial transfusion history, the impact of iron chelation on survival and disease progression is unknown.[
Disease-Modifying Agents
Lower-risk patients (conventionally defined as International Prognostic Scoring System (IPSS) low-risk and intermediate-1–risk groups) who have failed to respond or have ceased responding to ESAs may be treated with one of several disease-modifying agents. The impact of this practice on survival in lower-risk patients is unknown. Whether these drugs should be used following an ESA failure or as up-front therapy has never been determined. In contrast, in higher-risk patients, azacitidine has been shown to improve survival. For more information, see the DNA methyltransferase inhibitors section.
Lenalidomide
The U.S. Food and Drug Administration (FDA) approved lenalidomide for the treatment of lower-risk, transfusion-dependent patients with MDS who harbor a del(5q) cytogenic abnormality. In a phase II registration study of 148 transfusion-dependent low-risk and intermediate-1–risk patients with del(5q) chromosomal abnormalities (alone, or associated with other abnormalities), lenalidomide induced transfusion independence in 67%, with a median time to response of 4 to 5 weeks.[
Lenalidomide administration is limited by dose-limiting neutropenia and thrombocytopenia.[
A subsequent phase III study randomly assigned lower-risk del(5q) MDS patients to receive placebo and lenalidomide at either 5 mg daily for 28 days or 10 mg daily for 21 days of a 28-day cycle.[
Lenalidomide has limited activity in lower-risk, red blood cell transfusion–dependent patients in MDS who do not harbor the del(5q) lesion. In a phase II study similar in design to the registration study, 56 of 215 patients (26%) achieved transfusion independence.[
Immunosuppressive therapy
Antithymocyte globulin (ATG) has shown activity in MDS patients in several small series. The National Heart, Lung, and Blood Institute conducted a phase II trial including 25 MDS patients with less than 20% blasts. Of all the patients studied, 11 (or 44%) responded and became transfusion-independent after ATG (three complete responses, six partial responses, and two minimal responses).[
DNA methyltransferase inhibitors
The nucleoside analogues azacitidine and decitabine are inhibitors of DNA methyltransferase. Both drugs require prolonged administration before benefits are seen. The median number of cycles required to see first hematologic response to azacitidine was 3; 90% of responders showed response by 6 cycles; and the median number of cycles of decitabine required to see first response was 2.2.[
A phase III randomized controlled trial (AZA PH GL 2003 CL 001 [NCT00071799]) of azacitidine versus other regimens, including low-dose cytarabine, AML-type remission induction chemotherapy, or best supportive care, was limited to patients with higher-risk MDS subtypes (IPSS intermediate-2 risk and high risk).[
While the azacitidine congener decitabine demonstrated similar activity in phase II trials, two randomized trials of decitabine versus supportive care failed to show a survival benefit.[
Decitabine can be given as daily intravenous or subcutaneous infusions at doses that differ from the original labeled schedule, with hematologic response rates that appear comparable to the phase III study.[
Both of these drugs have been approved for refractory anemia, RARS (if accompanied by neutropenia or thrombocytopenia or requiring transfusions), refractory anemia with excess blasts, and refractory anemia with excess blasts in transformation. However, the highest response rates and levels of evidence have been generated in trials in which patients with higher-risk MDS (IPSS risk groups of intermediate-2 or high) were treated.[
Combinations of azacitidine with lenalidomide [
AML induction-type chemotherapy
Induction chemotherapy typically used to treat AML may be used to treat patients with higher-risk MDS with excess blasts.[
Allogeneic Hematopoietic Stem Cell Transplantation (HSCT)
Allogeneic HSCT is the only potentially curative treatment for MDS. Retrospective data suggest cure rates in selected patients ranging from 30% to 60%; outcomes varied with IPSS score at time of transplant, with inferior survival in patients with higher IPSS scores.[
Although HSCT represents the only treatment modality with curative potential, the relatively high morbidity and mortality of this approach limits its use. A decision analysis predating approval of azacitidine, in patients with a median age younger than 50 years, suggested optimal survival when transplant was delayed until disease progression for lower-risk patients but implemented at diagnosis for higher-risk patients.[
Allogeneic stem cell transplantation with reduced-intensity conditioning (RIC) has extended transplantation as a possible modality for treatment of older patients.[
Therapy-Related Myeloid Neoplasms
In the absence of prospective data, therapy-related myeloid neoplasms are treated similarly to de novo MDS.
Current Clinical Trials
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References:
Lack of response or progression after the use of erythropoiesis-stimulating agents is not considered relapsed or refractory myelodysplastic syndromes (MDS).
With the exception of the use of lenalidomide for low-risk patients with abnormalities of chromosome 5, there are no clinical trials informing the appropriate selection of therapies for patients with specific subtypes of MDS. Patients who have ceased to respond or did not respond to one therapy are frequently offered another from the therapies described in the previous sections. Retrospective data suggest that patients who do not respond or have ceased responding to DNA methyltransferase inhibitors have a median survival of only 4 to 6 months.[
Current Clinical Trials
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References:
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Last Revised: 2022-09-30
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