Chapter 25: Myelodysplastic Syndromes

INTRODUCTION

Myelodysplastic syndromes (MDS) represent premalignant entities that share many characteristics with acute myeloid leukemia (AML). These clonal hematopoietic stem cell (HSC) disorders are characterized by pancytopenia resulting from failure of normal hematopoiesis. The bone marrow shows hypercellularity, arrested maturation in one or more cellular lineages, and an increase in bone marrow myeloid precursors. Clinical symptoms result from cytopenias. Approximately one-third of patients ultimately progress to AML. Treatment involves supportive care and the use of agents capable of ameliorating cytopenias and delaying development of AML. However, hematopoietic stem cell transplantation (HCT) represents the only potentially curative treatment for MDS.

KEY FEATURES

• One or more peripheral blood cytopenias.

• Hematopoietic cell dysplasia.

• Bone marrow hypercellularity.

• Ringed sideroblasts in a subset of patients.

• Less than 20% bone marrow and peripheral blood myeloblasts.

• Abnormal cytogenetics are observed in approximately 50% of patients. Approximately 20% of patients have characteristic, interstitial deletions within the long arm of chromosome 5, which are associated with clinical response to immunomodulatory drugs (IMIDs).

• MDS may be related to prior chemotherapy and/or radiation for another medical condition (therapy-related MDS or T-MDS).

• Approximately 30% of patients with MDS develop AML.

EPIDEMIOLOGY

Approximately 15,000–30,000 new cases of MDS are diagnosed in the United States each year. MDS is three to four times more prevalent than AML and follows a more indolent course. MDS is likely underdiagnosed. MDS is one cause of anemia in the elderly.

ETIOLOGY

The exact cause of MDS is unknown in most patients. However, intrinsic defects in hematopoietic cells and extrinsic defects associated with the bone marrow microenvironment are involved in the pathogenesis of this disorder.

While most patients with MDS have spontaneously arising, de novo, disease, a portion of patients has therapy-related MDS (T-MDS). Such patients have received chemotherapy and/or radiation in the past, possibly for another malignancy or autoimmune disorder. T-MDS develops within a period of 3–10 years following chemotherapy and is associated with complex chromosomal abnormalities, often involving alterations of chromosomes 5 and/or 7. In addition, T-MDS is associated with a more aggressive clinical course and poorer prognosis in comparison to de novo MDS.

CLINICAL CHARACTERISTICS

• Median age is approximately 70 years.

• Slightly more common in males than in females.

• Prevalence is 50,000–100,000 cases in the United States.

• May be associated with prior chemotherapy, radiation, or environmental exposures to genotoxic agents.

CLASSIFICATION OF MDS

The World Health Organization (WHO) classification system includes refractory anemia (RA), RA with ringed sideroblasts (RARS), refractory cytopenia with multilineage dysplasia (RCMD), and MDS with isolated deletion of 5q for patients harboring a distinct interstitial deletion within the long arm of chromosome 5 (1). Patients with elevated bone marrow blasts of 5%–9% have RA with excess blasts I (RAEB-I) and ...