Types of Leukemia in Children?
Leukemia is described as being acute (rapidly growing) or chronic (slowly growing). Almost all childhood leukemia is acute.
Acute leukemia is divided into 2 types:
- acute lymphocytic leukemia (ALL, also called acute lymphoblastic leukemia)
- acute myelogenous leukemia (AML, also called acute myeloid leukemia, acute myelocytic leukemia, or acute non-lymphocytic leukemia [ANLL])
Chronic leukemias can also be divided into two types -- chronic lymphocytic leukemia (CLL) and chronic myelogenous leukemia (CML). These forms of leukemia are very rare in children and are not discussed in this document.
Most childhood leukemias are classified by how the cells look under the microscope. To help doctors see them clearly, the cells are stained, which changes the color of different parts of the cells. Although some leukemias can be easily classified by routine stains, most require special that help identify certain substances inside the leukemic cells.
Often more complex testing is needed to decide on the exact type of leukemia a child has. This is important, because different types of leukemia have a different prognosis (outlook) and are treated differently. Tests used to further classify leukemias include:
- a test that uses special antibodies to detect specific substances
on the cell surface or inside the cell.
- studies to detect changes in the chromosomes of cells.
- tests that show changes in the cell's DNA.
These tests are done on samples of leukemic cells from a child's blood or bone marrow, and are described in the section "How Is Childhood Acute Leukemia Diagnosed?"
Acute lymphocytic leukemia (ALL) is a cancer of the lymphocyte-forming cells called . In the past, ALL was divided into 3 major categories (L1 , L2, or L3) based on its morphology (appearance under the microscope).
- is the most common type in children. The lymphoblasts are small cells.
- accounts for 10% of ALL cases. The cells here are larger.
- is the rarest subtype.
This system is no longer used because there are better ways of classifying ALL than how it looks under the microscope. We include it here because some doctors may still refer to these categories. It is more useful to classify types of ALL by looking for certain substances, called antigens, in the cells. Tests for abnormalities in the genes and chromosomes of leukemia cells are also used to determine their type.
The leukemias are also further classified by their B- or T-cell status.
Type |
|
Early Pre-B |
57%-65% |
Pre-B |
20%-25% |
B Cell |
|
T Cell |
13%-15% |
The second type of B-cell leukemia subtype is the "pre-B" form of ALL. This form of ALL accounts for 20% to 25% of patients with B-cell ALL. The third and least common type of B-cell ALL is mature B-cell leukemia. This accounts for about 2% to 3% of childhood ALL. It is also called . Because this disease is essentially the same as Burkitt lymphoma and is treated differently than most leukemias, it is discussed in detail in our document "Non-Hodgkin Lymphoma in Children."
About 13% to 15% of children with ALL have T-cell ALL. This type of
leukemia affects boys more than girls, and generally affects children at an older age than B-cell ALL does. It is often associated with an enlarged thymus (which can sometimes cause breathing difficulty) and with early spread to the cerebrospinal fluid (the fluid that surrounds the brain and spinal cord).
Acute myelogenous leukemia (AML) is a cancer of one of the following types of early (immature) bone marrow cells:
- myeloblasts - these cells normally form granulocytes.
- monoblasts - these cells normally become monocytes.
- erythroblasts - these cells mature into red blood cells.
- megakaryoblasts - these cells normally become megakaryocytes, the cells that make platelets.
AML has several subtypes, depending on which type of these early cells develops into cancer. Although tests are often helpful in identifying AML, the subtypes of AML are classified almost exclusively by their morphology (appearance under the microscope), using routine and cytochemical stains. But more careful chemical testing may be useful to better determine the leukemia type. It is also useful to look for abnormalities in the chromosomes of the leukemia cells.
There are 8 subtypes of AML: MO to M7 (the "M" refers to myeloid).
- - This subtype of AML is made up of very . It can only be distinguished from ALL by flow cytometry because the leukemic cells lack any distinctive features that are apparent under the microscope (flow cytometry is explained in the section "How Is Childhood Leukemia Diagnosed?").
- , , and - These subtypes of AML are leukemias of and are recognized by their appearance under the microscope, particularly after applying cytochemical stains. The M3 subtype is known as acute promyelocytic leukemia (APL), and is treated differently from other types of AML.
- and - These are two forms of leukemia. These 2 types of AML are more likely to occur in children less than 2 years of age.
- - This subtype of AML is known as erythroleukemia. It develops in erythroblasts, the cells that normally mature into It is very rare in children.
- - This subtype is made up of leukemia cells and may show a unique "budding," resembling the way platelets normally form from normal mega karyocytes.
Some leukemias have features of both ALL and AML when the cells are viewed under a microscope and tested by flow cytometry or cytogenetic tests. They are generally treated like ALL and respond to treatment like ALL.
