Leukemia is a type of cancer that harms the body's ability to make healthy blood cells. It starts in the bone marrow, the soft center of various bones. This is where new blood cells are made. There are three main types of blood cells:
- red blood cells carry oxygen from the lungs to the body's tissues and take carbon dioxide to the lungs
- platelets help blood to clot
- white blood cells fight infections, viruses, and diseases
Leukemia usually refers to cancer of the white blood cells. It tends to affect one of the two major types of white blood cells: lymphocytes and granulocytes. These cells circulate through the bloodstream and the lymph system to help the body fight off viruses, infections, and other invading organisms. Leukemia arising from cancerous lymphocytes is called lymphocytic leukemia; leukemia from cancerous granulocytes is called myeloid or myelogenous leukemia.
Leukemia is either acute (comes on suddenly) or chronic (lasts a long time). Acute leukemia affects adults and children. Chronic leukemia rarely affects children.
Leukemia can occur due to
- genetic abnormalities
- exposure to radiation and chemicals such as benzene (found in unleaded gasoline) and other hydrocarbons
- exposure to agents used to cure or control other cancers, including radiation
Leukemia is usually not inherited. It tends to happen to people without any family history of the disease. Some forms of leukemia, though, such as chronic lymphocytic leukemia, strike close relatives in the same family.
In people who develop acute leukemia, immature white blood cells multiply quickly in the bone marrow. Over time, they crowd out healthy cells. This can cause unexpected or excessive bleeding or infections. When the cancerous white blood cells reach high numbers, they can spread to other organs, causing damage. This is especially true in acute myeloid leukemia.
The two main types of acute leukemia involve different types of blood cells:
- Acute lymphocytic leukemia is the most common type of leukemia in children. It mainly affects those under age 10, although adults sometimes develop it. Acute lymphocytic leukemia occurs when primitive blood-forming cells called lymphoblasts reproduce without developing into normal blood cells. These abnormal cells crowd out healthy blood cells. They can collect in the lymph nodes and cause swelling.
- Acute myeloid leukemia accounts for half of leukemia cases diagnosed in teenagers and in people in their 20s. It is the most common acute leukemia in adults. Acute myeloid leukemia occurs when primitive blood-forming cells called myeloblasts reproduce without developing into normal blood cells. Immature myeloblasts crowd the bone marrow and interfere with the production of normal blood cells. This leads to anemia, a condition in which a person does not have enough red blood cells. It can also lead to bleeding and bruising (due to a lack of blood platelets, which help the blood to clot) and frequent infections (due to a lack of protective white blood cells).
Both acute lymphocytic leukemia and acute myeloid leukemia have many subtypes. The treatment and prognosis may vary somewhat, depending on the subtype.
Chronic leukemia is when the body produces too many blood cells that are only partially developed. These cells often cannot function like mature blood cells. Chronic leukemia usually develops more slowly and is a less dramatic illness than acute leukemia. There are two main types of chronic leukemia:
- Chronic lymphocytic leukemia is rare in people under age 30. It is more likely to develop as a person ages. Most cases occur in people between ages 60 and 70. In chronic lymphocytic leukemia, abnormal lymphocytes can't fight infection as well as normal cells can. These cancerous cells live in the bone marrow, blood, spleen, and lymph nodes. They can cause swelling, which appears as swollen glands. People with chronic lymphocytic leukemia can live a long time, even without treatment. Most often, chronic lymphocytic leukemia is discovered when a person has a routine blood test that shows high levels of lymphocytes. Over time, this type of leukemia can require treatment, especially if the person has infections or develops a high white blood cell count.
- Chronic myeloid leukemia occurs most often in people between ages 25 and 60. In chronic myeloid leukemia, the abnormal cells are a type of blood cell called myeloid cells.
Both chronic lymphocytic leukemia and chronic myeloid leukemia have subtypes. They also share some characteristics with other forms of leukemia. The treatment and prognosis may vary depending on the subtype.
Rarer forms of leukemia
Lymphatic and myelogenous leukemias are the most common. However, cancers of other types of bone marrow cells can develop. Megakaryocytic leukemia arises from megakaryocytes, cells that form platelets. (Platelets help blood to clot.) Another rare form of leukemia is erythroleukemia. It arises from cells that that form red blood cells. Like chronic and acute leukemias, rare forms of the disease can be categorized into subtypes. The subtype depends on what markers the cells carry on their surface.
Early symptoms of leukemia include
- aching bones or joints
- skin rashes
- swollen glands (lymph nodes)
- unexplained weight loss
- bleeding or swollen gums
- an enlarged spleen or liver, or a feeling of abdominal fullness
- slow-healing cuts, nosebleeds, or frequent bruises
Leukemia can sometimes take a while to diagnose because many of its symptoms accompany the flu and other common medical problems.
Your doctor may not suspect leukemia based on your symptoms alone. However, during your physical examination, he or she may find that you have swollen lymph nodes or an enlarged liver or spleen. Routine blood tests, especially blood cell counts, may yield abnormal results.
At this point, your doctor may order other tests, including
- blood tests to check for abnormal cells
- a bone marrow biopsy (a sample of bone marrow is removed and examined)
- tests for genetic abnormalities
Genetic tests can help determine exactly what type of leukemia you have. These sophisticated tests may also offer clues as to how you will respond to a particular therapy.
The treatment of leukemia aims to wipe out the cancerous white blood cells. But this usually means killing healthy white blood cells and harming the body's ability to fight infection.
The treatment of acute leukemia does not depend on how far the disease has advanced but on the person's condition. Has the person just been diagnosed with the disease? Or has the disease come back after remission (a period when the disease is controlled)?
For acute lymphocytic leukemia, treatment generally occurs in phases:
- phase 1 uses chemotherapy in the hospital to try to control the disease.
- phase 2 continues chemotherapy, but on an outpatient basis, to keep the disease in remission. This means that person returns to the hospital for treatment, but does not stay overnight.
- phase 3 uses different chemotherapy drugs to prevent the leukemia from entering the brain and central nervous system. Chemotherapy may be combined with radiation therapy.
- phase 4 involves regular physical exams and laboratory tests after the leukemia has been treated to be sure that it has not returned.
If acute lymphocytic leukemia returns, different doses of various chemotherapy drugs are used to combat the disease. Several years of chemotherapy may be needed to keep the leukemia in remission. Some people may receive a bone marrow transplant.
With acute myeloid leukemia, treatment generally depends on the person's age and overall health. It also depends on his or her blood cell counts. As with acute lymphocytic leukemia, treatment usually begins with induction therapy in an effort to send the leukemia into remission. When leukemia cells can no longer be seen, consolidation therapy begins. Bone marrow transplantation may also be considered in the treatment plan.
Treatment for chronic lymphocytic leukemia begins with determining the extent of the cancer. This is called staging. There are five stages of chronic lymphocytic leukemia:
- stage 0: too many lymphocytes in the blood but no other symptoms
- stage I: lymph nodes are swollen because too many lymphocytes are being made
- stage II: lymph nodes, spleen, and liver are swollen because too many lymphocytes are being made
- stage III: anemia has developed because lymphocytes are crowding out red cells in the blood.
- stage IV: there are too few platelets in the blood. The lymph nodes, spleen, and liver may be swollen. Anemia may be present.
Treatment of chronic lymphocytic leukemia depends on the stage of the disease, as well as on the person's age and overall health. In stage 0, treatment may not be needed, but the person's health will be monitored closely. In stage I or II, observation (with close monitoring) or chemotherapy is the usual treatment. In Stage III or IV, intensive chemotherapy with one or more drugs is the standard treatment. Some people may need a bone marrow transplant.
For chronic myeloid leukemia, drugs known as tyrosine kinase inhibitors have become standard therapy, especially for people in the early stages of the disease. They correct the chemical defects in the cancer cells that had allowed them to grow in an uncontrollable fashion. The use of these targeted therapies has dramatically improved the prognosis for many people with chronic myeloid leukemia.