Leukemia is the most common form of cancer in childhood.
- It affects approximately 3,800 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 3. ALL accounts for about 73 percent leukemia cases each year in the U.S.
- 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.
What causes leukemia in children?
In nearly all cases, it is not known what causes leukemia. The majority of childhood leukemias are acquired genetic diseases. This means that gene mutations and chromosome abnormalities in leukemia cells occur sporadically (by chance). The abnormalities found in leukemia cells are not found in the other cells of the body.
The immune system plays an important role in protecting the body from disease, 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 infections have been associated with damage to the immune system, but none of these factors has been definitively linked as a cause of childhood leukemia.
What are the different types of leukemia?
There are three main types of leukemia, including the following:
- Acute lymphoblastic leukemia (ALL) - ALL, also called lymphocytic or lymphoid, accounts for about 75 to 80 percent of the childhood leukemias. In this form of the disease, the lymphocyte cell line is affected. The lymphocytes normally fight infection. With acute lymphoblastic 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) - AML, also called granulocytic, myelocytic, myeloblastic, or myeloid, accounts for about 20 percent 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) - 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 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.
It is thought that lymphoblastic and myelogenous leukemias differ based upon the stage of development of the cell in which the leukemia arises. 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 (lymphoblastic or myelogenous) is determined by where the cell is in its stage of development when it become malignant, or cancerous.
Early in its development, the stem cell becomes either a lymphocyte precursor cell or a myeloid precursor cell. The lymphoid cells mature into either B-lymphocytes or T-lymphocytes. If the leukemia develops in one of these cells, it is called acute lymphoblastic leukemia (ALL). It can be further classified as either B-cell precursor or T-cell ALL, depending on the type of lymphoid precursor cell. If the leukemia is found even further along this stage of development, it is sometimes referred to as a mature B-cell ALL or T-cell ALL.
The myeloid cells develop into platelets, red blood cells and specialized white blood cells called nurtrophils and macrophages. There are many classifications of AML. The types of leukemia is determined by the stage of development when the normal cells become leukemia cells.
What are the symptoms of leukemia?
Because leukemia is cancer of the blood-forming tissue called the bone marrow, the initial symptoms are often related to abnormal bone marrow function. The bone marrow is responsible for storing and producing about 95 percent 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:
- anemia - 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. Petechia are tiny red dots often seen on the skin of a child with low number of platelets. Petechia 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, and 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.