Leukemia is cancer of the blood and develops in the bone marrow. The bone marrow is the soft, spongy center of certain bones that produces the three major blood cells: white blood cells to fight infection; red blood cells that carry oxygen; and platelets that help with blood clotting and stop bleeding. When a child has leukemia, the bone marrow, for an unknown reason, begins to make white blood cells that do not mature correctly, but continue to reproduce themselves. Normal, healthy cells only reproduce when there is enough space for them to fit. The body can regulate the production of cells by sending signals when to stop. With leukemia, these cells do not respond to the signals to stop and reproduce, regardless of space available.
These abnormal cells reproduce very quickly and do not function as healthy white blood cells to help fight infection. When the immature white blood cells, called blasts, begin to crowd out other healthy cells in the bone marrow, the child experiences the symptoms of leukemia (such as infections, anemia, or bleeding).
Leukemia is the most common form of cancer in childhood. It affects approximately 3,500 children each year in the US, accounting for about 30 percent of childhood cancers.
There are different types of leukemia. According to the American Cancer Society, acute lymphocytic leukemia (ALL) is the type of leukemia that most commonly affects children, most often between the ages of 2 and 4 years. Acute myelogenous leukemia (AML) is the second most common form of leukemia in children. AML generally occurs by the age of 2 years, and is not often seen in older children until the teenage years. AML is the most common type of acute leukemia in adults. The chronic forms of leukemia are rarely seen in children.
The majority of childhood leukemias are acquired diseases. This means that gene mutations and chromosome abnormalities in cells occur sporadically (by chance) and are not inherited from a parent.
The immune system plays an important role in protecting the body from diseases, and possibly cancer. An alteration or defect in the immune system may increase the risk for developing leukemia. Factors such as exposure to certain viruses, environmental factors, chemical exposures, and various infections have been associated with damage to the immune system.
With the exception of specific genetic syndromes, little is known about the causes of childhood leukemia.
There are three main types of leukemia in children:
- Acute lymphocytic leukemia (ALL)
Acute lymphocytic leukemia (ALL), also called lymphoblastic or lymphoid, accounts for most of the childhood leukemias. In this form of the disease, the lymphocyte cell line is affected. The lymphocytes normally fight infection. With acute lymphocytic leukemia, the bone marrow makes too many of these lymphocytes and they do not mature correctly. The lymphocytes overproduce, thus, crowding out other blood cells. Immature blood cells (blasts) do not work properly to fight infection. Acute leukemia can occur over a short period of days to weeks. Chromosome abnormalities (extra chromosomes and structural changes in the chromosome material) are present in the majority of ALL patients.
- Acute myelogenous leukemia (AML)
Acute myelogenous leukemia (AML), also called granulocytic, myelocytic, myeloblastic, or myeloid, accounts for most of the remainder of the childhood leukemias. Acute myelogenous leukemia is a cancer of the blood in which too many granulocytes, a type of white blood cell, are produced in the marrow. The granulocytes normally fight infection. With acute myelogenous leukemia, the bone marrow makes too many of these cells and they do not mature correctly. The granulocytes overproduce, thus, crowding out other blood cells. Immature blood cells (blasts) do not work properly to fight infection. Acute leukemia can occur over a short period of days to weeks. Children with certain genetic syndromes, including Fanconi anemia, Bloom syndrome, Kostmann syndrome, and Down syndrome, are at a higher risk of developing AML than other children.
- Chronic myelogenous leukemia (CML)
Chronic myelogenous leukemia (CML) is uncommon in children. Chronic myelogenous leukemia is cancer of the blood in which too many granulocytes, a type of white blood cell, are produced in the marrow. The granulocytes normally fight infection. With this disease, the bone marrow makes too many of these cells and they do not mature correctly. The marrow continues to produce these abnormal cells which crowd out other healthy blood cells. Chronic myelogenous leukemia can occur over a period of months or years. A specific chromosome rearrangement is found in almost all patients with CML. Part of chromosome #9 breaks off and attaches itself to chromosome #22, so that there is an exchange of genetic material between these two chromosomes. This rearrangement changes the position and functions of certain genes, which results in uncontrolled cell growth. Other chromosome abnormalities can also be present.
The difference between lymphocytic and myelogenous is the stage of development on what is called the pluripotent stem cell. The pluripotent stem cell is the first stage of development of all of the blood cells (white blood cells, red blood cells, and platelets). This stem cell goes through stages of development until it matures into a functioning cell. The type of leukemia is determined by where the cell is in the stage of development when it becomes malignant, or cancerous.
The stem cell matures into either the lymphoid or myeloid cells. The lymphoid cells mature into either B-lymphocytes or T-lymphocytes. If the leukemia is among these cells, it is called acute lymphocytic leukemia (ALL). If the leukemia is found even further along this stage of development, it can be further classified as B-cell ALL or T-cell ALL. The more mature the cell, the more difficult it is to treat.
The myeloid cells develop into platelets, red blood cells, and specialized white blood cells, such as neutrophils and macrophages. There are many classifications of AML. The type of leukemia is determined by the stage of development when the normal cells become leukemia cells.
Because leukemia is cancer of the blood-forming tissue called the bone marrow, the initial symptoms are often related to irregular bone marrow function. The bone marrow is responsible for producing most of the body's blood cells, including the red blood cells, white blood cells, and platelets.
When leukemia occurs, the abnormal white blood cells (blasts) begin to reproduce very rapidly and begin crowding out and competing for nutrients and space with the other healthy cells. The following are the most common symptoms of leukemia. However, each child may experience symptoms differently. Symptoms may include:
When red blood cells are unable to be produced because of the crowding in the marrow, anemia is present. With anemia, the child may appear tired, pale, and may breathe faster to compensate for the decrease in oxygen carrying capacity. The number of red blood cells on a blood count will be below normal.
- Bleeding and/or bruising
When platelets are unable to be produced because of the crowding in the marrow, bleeding can occur and the child may begin to bruise more easily. Petechiae are tiny red dots often seen on the skin of a child with low number of platelets. Petechiae are very small blood vessels that have "leaked" or bled. The number of platelets on a blood count will be below normal. Thrombocytopenia is the term used for a decreased number of platelets.
- Recurrent infections
Although there may be an unusually high number of white blood cells on a blood count of a child with leukemia, these white blood cells are immature and do not fight infection. The child may have had repetitive viral or bacterial infections over the past few weeks. The child with leukemia often shows symptoms of an infection such as fever, runny nose, and cough.
- Bone and joint pain
Pain in bones and joints is another common symptom of leukemia. This pain is usually a result of the bone marrow being overcrowded and "full."
- Abdominal distress
Abdominal pain may also be a symptom of leukemia. Leukemia cells can collect in the kidney, liver, and spleen, causing enlargement of these organs. Pain in the abdomen may cause a child to have loss of appetite and weight loss.
- Swollen lymph nodes
The child may also have swelling in the lymph nodes under the arms, in the groin, chest, or in the neck. Lymph nodes are responsible for filtering the blood. Leukemia cells may collect in the nodes, causing swelling.
- Difficulty breathing (dyspnea)
With T-cell ALL, these leukemia cells tend to clump together around the thymus. This mass of cells present in the middle of the chest can cause pain and difficulty breathing (dyspnea). Wheezing, coughing, and/or painful breathing requires immediate medical attention.
With acute leukemia (ALL or AML), these symptoms may occur suddenly in a matter of days or weeks. With chronic leukemia (CML), these symptoms may develop slowly over months to years.
It is important to understand that the symptoms of leukemia may resemble other blood disorders or medical problems. These are common symptoms of the disease, but do not include all possible symptoms. Children may experience symptoms differently. Always consult your child's physician for a diagnosis.
In addition to a complete medical history and physical examination, diagnostic procedures for leukemia may include:
- Bone marrow aspiration and/or biopsy - a procedure that involves taking a small amount of bone marrow fluid (aspiration) and/or solid bone marrow tissue (called a core biopsy), usually from the hip bones, to be examined for the number, size, and maturity of blood cells and/or abnormal cells.
- Complete blood count (CBC) - a measurement of size, number, and maturity of different blood cells in a specific volume of blood.
- Additional blood tests - may include blood chemistries, evaluation of liver and kidney functions, and genetic studies.
- Computed tomography scan (also called a CT or CAT scan) - a diagnostic imaging procedure that uses a combination of x-rays and computer technology to produce cross-sectional images (often called slices), both horizontally and vertically, of the body. A CT scan shows detailed images of any part of the body, including the bones, muscles, fat, and organs. CT scans are more detailed than general x-rays.
- Magnetic resonance imaging (MRI) - a diagnostic procedure that uses a combination of large magnets, radiofrequencies, and a computer to produce detailed images of organs and structures within the body.
- X-ray - a diagnostic test that uses invisible electromagnetic energy beams to produce images of internal tissues, bones, and organs onto film.
- Ultrasound (also called sonography) - a diagnostic imaging technique that uses high-frequency sound waves and a computer to create images of blood vessels, tissues, and organs. Ultrasounds are used to view internal organs as they function, and to assess blood flow through various vessels.
- Lymph node biopsy - a sample of tissue is removed from the lymph node and examined under a microscope.
- Spinal tap/lumbar puncture - a special needle is placed into the lower back, into the spinal canal. This is the area around the spinal cord. The pressure in the spinal canal and brain can then be measured. A small amount of cerebral spinal fluid (CSF) can be removed and sent for testing to determine if there are leukemia cells, an infection, or other problems. CSF is the fluid that bathes your child's brain and spinal cord.
Specific treatment for leukemia will be determined by your child's physician based on:
- Your child's age, overall health, and medical history
- The type of leukemia and other factors, such as chromosome changes in the leukemia cells
- The extent of the disease
- Your child's tolerance for certain medications, procedures, or therapies
- Expectations for the course of the disease
- Your opinion or preference
Treatment usually begins by addressing the presenting symptoms such as anemia, bleeding, and/or infection. In addition, treatment for leukemia may include (alone or in combination) the following:
- Intrathecal medications/chemotherapy (medications are inserted through a needle into the spinal cord to help prevent or treat leukemia in the brain or spinal cord)
- Radiation therapy
- Bone marrow transplantation or peripheral blood stem cell transplantation
- Targeted therapy
- Surgery (rarely)
- Medications (to prevent or treat damage to other systems of the body caused by leukemia treatment)
- Medications (for nausea and side effects of treatment)
- Blood transfusions (red blood cells, platelets)
- Antibiotics (to prevent/treat infections)
- Continuous follow-up care (to determine response to treatment, detect recurrent disease, and manage late effects of treatment)
There are various stages in the treatment of acute leukemia, including the following:
- Induction - a combination of chemotherapy and/or radiation and medications given to stop the process of abnormal cells being made in the bone marrow. Remission is the goal in this stage of treatment. Remission means the leukemia cells are no longer being made. This phase may last approximately one month and can be repeated if the goal is not achieved.
- Intensification (consolidation) - continued treatment even though leukemia cells may not be visible. The leukemia cells may not be visible in a blood test or bone marrow examination, but it is possible that the cells are still present in the body.
- Maintenance - the stage that maintains leukemia-free bone marrow by continuing less intense chemotherapy for a longer duration. This phase is used for ALL but not for AML. It can last months to several years. Regular visits to your child's physician are required in order to determine response to treatment, detect any recurrent disease, and manage any side effects of the treatment.
Relapse may occur even with aggressive therapy. Relapse is when the bone marrow begins making abnormal cells again. Relapse can occur during any of the stages of treatment, or may occur months or years after treatment has ended.
Treatment for chronic myelogenous leukemia may begin with a targeted therapy drug. These drugs are usually very effective at keeping the leukemia under control, but because they do not cure it and they must be taken continuously, the doctor may recommend a stem cell transplant, if one can be done.
Prognosis greatly depends on:
- The type and extent of the disease
- Disease response to treatment
- Age and overall health of the child
- Your child's tolerance of specific medications, procedures, or therapies
- New developments in treatment
As with any cancer, prognosis and long-term survival can vary greatly from child to child. Prompt medical attention and aggressive therapy are important for the best prognosis. Continuous follow-up care is essential for the child diagnosed with leukemia.
Side effects of radiation and chemotherapy, as well as second malignancies, can occur in survivors of leukemia. New methods are continually being discovered to improve treatment and to decrease side effects of the treatment for the disease.