Types of AML: classification and identification

Acute myeloid leukemia (AML) is a type of cancer that starts in hematopoietic cells in the bone marrow. Doctors do not stage AML like many other cancers because it usually does not form tumors. Instead, experts can categorize AML into subtypes, which can help them provide the most appropriate treatments.

AML is the most common type of acute leukemia in adults. Some research estimates that 20 240 people will be diagnosed with AML in 2021.

Some people may refer to AML as acute myeloid leukemia, acute myelogenous leukemia, acute granulocytic leukemia, or acute non-lymphocytic leukemia.

Doctors can use classification systems to classify AML subtypes based on specific characteristics of blood cells. By identifying the subtype and prognostic factors, such as age, doctors can suggest the best treatment options and improve a person’s outlook.

This article discusses AML, including its subtypes according to the two most commonly used classification systems for AML. It also examines the identification, outlook and risk of AML relapse.

The Franco-American-British (FAB) classification for acute leukemia is an older classification system that people have been using since the 1970s. However, doctors still use it commonly today.

This classification system is based on how cells appear under a microscope. Knowing this helps doctors identify their cell line and degree of maturation.

The FAB classification divides AML into subtypes M0 to M7 as follows:

  • M0: undifferentiated acute myelogenous leukemia
  • M1: acute myelogenous leukemia with little or no maturation
  • M2: acute myelogenous leukemia with maturation
  • M3: acute promyelocytic leukemia (APL)
  • M4: acute myelomonocytic leukemia
  • M4éo: acute myelomonocytic leukemia with eosinophilia
  • M5: acute monocytic leukemia
  • M6: acute erythroid leukemia
  • M7: acute megakaryoblastic leukemia

The World Health Organization (WHO) classification for AML is the most recent and widely used system for classifying AML.

Unlike the FAB classification, the WHO classification takes into account factors that affect a person’s outlook. Features such as genetic irregularities, biological features, and the effects of prior exposure to treatment all affect the clinical presentation and outlook for AML.

The WHO Classification of Tumors, 4th revised edition, volume 2 – published in 2017 – divides AML into the following general groups:

  • AML with recurrent genetic abnormalities
  • AML with changes related to myelodysplasia
  • treatment-related myeloid neoplasms
  • AML not otherwise specified
  • myeloid sarcoma
  • myeloid proliferations associated with Down syndrome

Doctors can identify the specific type of AML by testing leukemia cells in the person’s bone marrow and blood samples.

Specifically, specialists use tests to examine their shape, size and appearance (morphology), cell components and composition (cytochemistry), and the presence of markers, or antigens, on the cell surface to determine their function. (immunophenotyping).

These tests include:

  • Peripheral blood smear: An expert will examine a blood sample under a microscope to identify changes in the number and appearance of different types of blood cells.
  • Cytochemistry: This test uses dyes to cause some leukemia cells to change color. This can help specialists determine what types of cells are present in the sample.
  • Immunophenotyping: This test is essential for classifying AML by examining markers, or antigens, on the cell surface to help determine what type of cell they start in and how mature they are.
  • Cytogenetic : This chromosome test looks at cells under a microscope to see if a person’s chromosomes have irregularities. Chromosome changes that this test can detect include translocations, inversions, deletions, additions, and duplications.
  • Fluorescent in situ hybridization: This is another chromosome test that uses special fluorescent dyes that only attach to certain parts of the chromosomes or to specific genes.
  • Polymerase chain reaction: This is a sensitive test that can identify changes too small for an expert to see under a microscope. It is useful for detecting the presence of a low number of leukemia cells in a sample.

People with AML respond variably to treatment due to the diversity of genetic and clinical presentations. Some factors that affect the outlook for AML include a person’s AML subtype, age, and response to treatment. The sections below examine each of these factors in more detail.

Age

People over 60 usually have a more unfavorable outlook than younger individuals. This may be because older people have more chromosomal irregularities and other medical conditions.

Response to initial treatment

People who respond well to treatment and achieve complete remission on initial treatment usually have better survival results than those who do not respond to treatment or who relapse within the first 6 months.

Chromosomal irregularities

About 50-60% of people with AML have cytogenetic irregularities. Some cytogenetic or chromosomal irregularities are associated with better results, while others may suggest poorer results.

For example, APL is a subtype of AML. The FAB classification classifies it as an M3 subtype, and the WHO classification classifies it as APL with a translocation between chromosomes 15 and 17.

Due to advances in diagnostic techniques and treatments, many experts consider APL to be one of the most curable subtypes of AML in adults. It has complete remission and cure rates of around 90% and 80%, respectively.

Genetic mutations

Some research indicates that genetic mutations can affect how people respond to certain treatments, with some mutations being associated with better results.

For example, having mutations in the NPM1 uncomfortable is associated with a higher likelihood of complete remission, improved overall survival, and a lower incidence of relapse.

Meanwhile, testimonials from European LeukemiaNet indicates that mutations in the TP53 gene are associated with particularly low survival rates.

Markers in leukemia cells

Doctors also use antigens in leukemia cells to determine the prognosis. People who strongly express CD56 generally have a poorer outlook and lower overall survival rates.

Some research also suggests that people with peripheral blood blasts with elevated CD87 expression also have a poorer outlook and are likely to relapse.

Other conditions

People with a history of myelodysplastic syndrome or another blood disorder and people who develop AML as a result of treatments for other types of cancer, known as treatment-related AML, also have poorer health outcomes. perspectives.

AML is a type of leukemia with many subtypes that have different clinical presentations and respond to treatment differently due to many different factors.

Classification systems can identify subtypes of AML on the basis of these clinical features and characteristics, which are useful in determining the diagnosis, treatment, and outlook of people with AML.

Besides the subtype of AML, other factors affecting outlook, such as age and the presence of genetic mutations, may impact the outcome of AML. Although treatment advances lead to a better outlook, people with AML – including those who have achieved complete remission after their initial treatment – may still be at risk for a relapse.


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