The Children’s Mercy Leukemia and Lymphoma Program has compiled the following information for families who want to better understand the types, causes and treatments for leukemia. You can also visit the Children’s Mercy Health Library or the Leukemia and Lymphoma Society for more information.
What is leukemia?
Leukemia is a cancer of the white blood cells. It is the most common cancer diagnosis seen in children and affects approximately 4,000 children every year in the United States.
Since white blood cells are made in the bone marrow, this is where leukemia begins. When white blood cells become cancerous, they begin to grow very rapidly. Most patients diagnosed with pediatric leukemia have only had symptoms for days or weeks.
In children who have leukemia, the bone marrow begins to fill with leukemia cells. When someone is diagnosed with leukemia, these cells can often be seen in the blood when laboratory testing is requested.
At the time leukemia is diagnosed, there are usually over 100 billion leukemia cells throughout the body. The large number of leukemia cells in the bone marrow prevent the body from making healthy white blood cells, red blood cells and platelets. This accounts for many of the symptoms of leukemia, including bruising, bleeding, fatigue, and having pale skin.
Leukemia can often involve other areas of the body including the lymph nodes, the liver and the spleen.
Causes of leukemia
Leukemia is caused by genetic mutations that occur in a single white blood cell that result in the loss of normal function and cause the cell to grow and divide very rapidly. In the majority of cases, these mutations occur randomly and are not inherited from family members. For most cases of childhood leukemia, a cause cannot be identified.
There are a few things that can place a child at increased risk for leukemia. Some genetic conditions are associated with a higher chance that a child may develop leukemia. Some examples are Down syndrome, Fanconi anemia and Li-Fraumeni syndrome. A weakened immune system and previous exposure to certain types of chemotherapy or radiation therapy may place children at increased risk of developing leukemia.
Symptoms of leukemia
When leukemia is discovered in children, symptoms have typically been present for days to weeks. Fever is a common complaint with leukemia, and frequently children are thought to have an infection before leukemia is discovered.
Many patients with leukemia develop anemia as the leukemia cells prevent the body from making red blood cells. This can cause fatigue and lead to pale skin. Patients also have trouble making platelets, which are cells that help the blood to clot. Therefore, bruising and bleeding are frequent symptoms of leukemia. A rash can also develop that consists of many small red dots called petechiae that are caused by tiny amounts of bleeding from very small blood vessels.
As leukemia cells grow rapidly in the bone marrow, they can cause bone pain and difficulty walking or limping. Other symptoms of leukemia include swollen lymph nodes or an enlarged liver and/or spleen.
The first test to determine if a child has leukemia is a Complete Blood Count (CBC). This provides the number of white blood cells, red blood cells and platelets that are in the blood.
In most patients with leukemia, the leukemia cells (also called blasts) can be seen in the blood and may lead to a higher than normal white blood cell number. In some cases, blasts are not present in the blood, but low numbers of white blood cells, red blood cells and platelets may be suggestive of leukemia. In these cases, testing of the bone marrow is performed to look for leukemia cells.
Once it is determined that a child has leukemia, there are additional tests that need to be done to further define the leukemia to ensure that the optimal treatment is given.
If leukemia is diagnosed or suspected based on the CBC, the blood or bone marrow is analyzed by a flow cytometer. The flow cytometer is able to detect the proteins on the surface of blood cells. In the case of leukemia, since the leukemia cells all originate from the same abnormal cell, the flow cytometer can identify a population of cells that are identical and have the same proteins on their cell surface. The type of proteins expressed can tell us what type of leukemia a patient has.
Once a diagnosis of leukemia has been established, it is important to know if there is leukemia in the central nervous system (CNS). A lumbar puncture or spinal tap is done to get cerebrospinal fluid (CSF) that is then analyzed for the presence of leukemia cells.
Leukemia cells obtained from the blood or bone marrow are sent for additional testing to look for specific genetic mutations that may indicate whether the leukemia is more or less likely to respond to chemotherapy. The results of these tests can have an impact on what therapy is needed to cure the leukemia.
Types of leukemia
Acute Lymphoblastic Leukemia (ALL)
This is the most common type of leukemia in children. Approximately 75% of children diagnosed with leukemia during childhood will have ALL. In patients with ALL, the cancer starts in a type of white blood cells called a lymphocyte. ALL is most likely to occur in children between the ages of 2 and 5, although it occurs in children and adolescents of all ages.
ALL is very treatable with modern regimens, and approximately 90% of children diagnosed with ALL will achieve a long-term cure.
ALL is divided into Precursor B-Cell and T-Cell ALL based on the presence of certain proteins on the surface of the leukemia cells that are detected using a flow cytometry test. Both types of ALL are treated similarly, with Precursor B-Cell patients having a slightly more favorable outcome, often with less aggressive treatment. Patients with T-cell ALL are more likely to have enlarged lymph nodes, a large chest mass that causes difficulty breathing and/or leukemia cells present in the central nervous system at diagnosis.
Acute Myelogenous Leukemia (AML)
This is the second most common type of leukemia in children. Around 20% of children diagnosed with leukemia will have AML. AML develops from immature blood cells and is classified into subtypes from M0 to M7 based on the type of immature blood cell where the cancer starts.
M3 AML is a unique subtype referred to as acute promyelocytic leukemia or APL. AML is treatable with chemotherapy, with long-term survival rates around 65%. Children diagnosed with APL have excellent survival in excess of 85% using targeted therapy.
Mixed Lineage or Biphenotypic Leukemia
This is diagnosed when leukemia cells have features of both ALL and AML. This is rare and makes up only about 1% of all leukemia diagnoses.
Chronic Myelogenous Leukemia (CML)
CML is rare in children, and makes up only about 3% of all leukemia diagnosed in children. Children with CML often have a very high white blood count and a large spleen at diagnosis. CML is a unique disease where the leukemia cells have a very specific genetic mutation called the ‘Philadelphia chromosome.’
CML is one of the few cancers in which targeted therapy alone has been very effective. Most children with CML respond very well to oral medications that target the genetics of the disease. The majority of children with CML will stay on their medications indefinitely. Currently, hematopoietic stem cell transplantation is the only curative treatment of CML but this is typically used only for patients who do not respond to treatment.
Juvenile Myelomonocytic Leukemia (JMML)
JMML is a very rare type of leukemia that occurs most often in very young children. Children with JMML usually have a high white blood count and an enlarged spleen. JMML requires a hematopoietic stem cell transplant (also called a bone marrow transplant) in order to be cured.