Acute Myeloid Leukemia (AML) is a rapidly progressing cancer originating in the bone marrow, the tissue responsible for blood cell production. The disease is characterized by the presence of abnormal, immature white blood cells known as “blasts.” These blasts are the cancerous cells themselves, multiplying uncontrollably and failing to mature into functional blood components. Understanding their behavior is necessary to grasp how AML affects the body and how it is treated.
What Are Myeloid Blasts?
Myeloid blasts are the earliest, most immature forms of cells within the bone marrow’s myeloid lineage. Normally, these progenitor cells would mature into various healthy blood components, including red blood cells, platelets, and several types of white blood cells like neutrophils and monocytes. In a healthy individual, the bone marrow contains less than 5% blasts, which are rarely seen in the circulating bloodstream. The normal development process, called hematopoiesis, is a tightly regulated system that ensures a constant supply of functional cells to the body.
In Acute Myeloid Leukemia, a genetic change occurs within a myeloid progenitor cell, causing it to become malignant. This mutation leads to two primary problems: a failure to mature, known as differentiation arrest, and rapid, uncontrolled multiplication. The resulting abnormal cells, the AML blasts, are essentially stuck in an early, non-functional stage of development. They ignore the body’s signals to stop dividing or to undergo programmed cell death, allowing them to accumulate in the bone marrow and blood.
How AML Blasts Disrupt Normal Blood Production
The principal mechanism by which AML blasts harm the body is through “crowding out” the normal hematopoietic environment. As the abnormal blasts rapidly proliferate, they physically take up space within the confined bone marrow. This overwhelming presence of leukemic cells prevents the bone marrow from producing adequate numbers of healthy, mature blood cells.
The resulting lack of normal blood components causes the main physical manifestations of the disease. A deficiency in healthy red blood cells, known as anemia, often leads to symptoms like extreme fatigue, weakness, and paleness because oxygen delivery throughout the body is impaired. Similarly, the absence of functional white blood cells, specifically neutrophils, severely compromises the immune system, leading to an increased risk of frequent or severe infections. A low platelet count, or thrombocytopenia, interferes with the blood’s clotting ability, resulting in easy bruising, bleeding gums, and tiny red spots on the skin called petechiae.
Identifying and Quantifying AML Blasts
Diagnosing AML begins with routine blood tests, such as a complete blood count, which may reveal low numbers of healthy mature cells and the presence of blasts in the peripheral blood. Since the disease originates in the bone marrow, a definitive diagnosis requires a bone marrow aspiration and biopsy. This procedure involves collecting a small sample of the spongy tissue, typically from the hip bone, for laboratory analysis.
In the lab, the sample is examined under a microscope to count the percentage of blasts present. A diagnosis of AML is confirmed if 20% or more of the cells in the bone marrow or blood are blasts. This percentage is a defining threshold, though specific genetic abnormalities can qualify a case as AML regardless of the blast count. Specialized tests like flow cytometry identify specific proteins on the surface of the blasts, which helps classify the subtype of AML and guides treatment decisions.
The Role of Blasts in Guiding Treatment
The blast count serves as the primary metric for monitoring disease status and determining treatment effectiveness. The goal of initial treatment is cytoreduction, the rapid destruction of the proliferating blast population in the bone marrow. This therapy aims to clear the bone marrow so that normal blood cell production can resume.
The most common measure of treatment success is achieving “complete remission.” This is defined by two main criteria: the recovery of normal blood cell counts and the reduction of blasts to less than 5% of the cells in the bone marrow. If the blast percentage remains above this threshold, the disease is considered active or persistent. Ongoing monitoring of the blast level is essential to confirm treatment effectiveness, detect potential relapse, or determine if a patient needs a more intensive intervention, such as a stem cell transplant.