Myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML) are disorders originating in the bone marrow that disrupt the normal production of blood cells. They specifically involve the myeloid line of cells, which are responsible for generating red blood cells, platelets, and most types of white blood cells. While they share this common origin and can present with similar symptoms, they are distinct conditions with different diagnostic criteria, progression patterns, and treatment strategies.
Defining Myelodysplastic Syndromes
Myelodysplastic syndromes are cancers where immature blood cells in the bone marrow fail to develop into healthy, functional cells. This disordered development, known as dysplasia, means the cells produced are abnormal in shape, size, and appearance. Many of these defective cells die within the bone marrow or shortly after entering the bloodstream, leading to a shortage of one or more types of blood cells.
These shortages, called cytopenias, are a defining feature of MDS and cause most of its symptoms. A low red blood cell count (anemia) can lead to fatigue, weakness, and shortness of breath. A deficiency in healthy white blood cells (neutropenia) impairs the body’s ability to fight infections, while a low platelet count (thrombocytopenia) can result in easy bruising and bleeding. MDS is a disease of older adults, with most patients being over the age of 65.
Defining Acute Myeloid Leukemia
Acute myeloid leukemia is a cancer defined by the rapid production of abnormal, immature myeloid cells known as myeloblasts. These malignant cells accumulate quickly in the bone marrow, suppressing the production of all normal blood cells and causing a swift decline in healthy red cells, white cells, and platelets.
This process leads to symptoms similar to those of MDS. However, the distinction with AML is its “acute” nature; the disease progresses very rapidly, and the onset of severe symptoms can occur over weeks or even days. This rapid progression means that AML is fatal within a short period if left untreated and requires immediate medical intervention.
Key Diagnostic Distinctions
The distinction between MDS and AML rests on the percentage of blast cells found in the bone marrow. The World Health Organization (WHO) has established that a diagnosis of AML is made when the bone marrow or blood contains 20% or more blast cells. If the blast count is below this 20% mark and other criteria are met, the diagnosis is MDS. This measurement is obtained through a bone marrow aspirate and biopsy, procedures where a small sample of bone marrow liquid and tissue is removed for microscopic examination.
Beyond this blast count, doctors use other diagnostic tools to predict the disease’s behavior. Cytogenetic analysis examines the cells for large-scale chromosomal abnormalities, such as deletions or rearrangements of genetic material. Molecular testing searches for specific mutations in the DNA of the cancer cells, which can influence both prognosis and treatment decisions for MDS and AML.
The Connection and Progression
The relationship between MDS and AML is direct, as MDS is considered a pre-leukemic condition. Many individuals diagnosed with MDS, particularly those with higher-risk forms of the disease, will eventually have their condition transform into AML. This progression occurs because the abnormal cells in the bone marrow continue to acquire additional genetic mutations over time.
These new mutations can accelerate the proliferation of abnormal cells and block their ability to mature, causing the blast percentage to rise. Once the proportion of blasts reaches or exceeds the 20% threshold, the diagnosis officially changes from MDS to AML. It is estimated that about one-third of patients with MDS will ultimately progress to AML. This transformation often results in a more aggressive disease that is resistant to treatment.
Contrasting Treatment Approaches
The treatment strategies for MDS and AML differ, reflecting the distinct nature and pace of each disease. For lower-risk MDS, where the primary issue is low blood counts, the approach is less aggressive. Treatment focuses on supportive care, such as blood transfusions to manage anemia or platelet deficiencies, and medications called growth factors to stimulate the production of healthy blood cells. For higher-risk MDS, treatment involves lower-intensity chemotherapy with drugs known as hypomethylating agents to slow disease progression.
In contrast, a diagnosis of AML necessitates immediate and intensive treatment. The standard approach is induction chemotherapy, a regimen designed to destroy the leukemia cells and induce a remission. Allogeneic stem cell transplantation, which replaces the patient’s diseased marrow with healthy cells from a donor, can be a curative option for both conditions. However, timing and eligibility for a transplant are determined by the specific diagnosis, the patient’s overall health, and the genetic risk profile of the disease.