leukemia

Leukemia is any of a group of cancers in which the bone marrow and other blood-forming tissues produce abnormal numbers of immature or defective leukocytes (white blood cells). This overproduction suppresses output of normal blood cells and platelets, leaving the person vulnerable to infection, anemia, and bleeding. Leukemias are classified into acute and chronic forms and also according to the type of leukocyte involved.

Types of leukemia

The types of leukemia are grouped by how quickly the disease develops and gets worse. Leukemia is either chronic (gets worse slowly) or acute (gets worse quickly):

Chronic leukemia. Early in the disease, the abnormal blood cells can still do their work, and people with chronic leukemia may not have any symptoms. Slowly, chronic leukemia gets worse. It causes symptoms as the number of leukemia cells in the blood rises.

Acute leukemia. The blood cells are very abnormal. They cannot carry out their normal work. The number of abnormal cells increases rapidly. Acute leukemia worsens quickly.

The types of leukemia are also grouped by the type of white blood cell that is affected. Leukemia can arise in lymphoid cells or myeloid cells. Leukemia that affects lymphoid cells is called lymphocytic leukemia. Leukemia that affects myeloid cells is called myeloid leukemia or myelogenous leukemia.

There are four common types of leukemia:

Chronic lymphocytic leukemia (chronic lymphoblastic leukemia, CLL) accounts for about 7,000 new cases of leukemia each year. Most often, people diagnosed with the disease are over age 55. It almost never affects children.

Chronic myeloid leukemia (chronic myelogenous leukemia, CML) accounts for about 4,400 new cases of leukemia each year. It affects mainly adults.

Acute lymphocytic leukemia (acute lymphoblastic leukemia, ALL) accounts for about 3,800 new cases of leukemia each year. It is the most common type of leukemia in young children. It also affects adults.

Acute myeloid leukemia (acute myelogenous leukemia, AML) accounts for about 10,600 new cases of leukemia each year. It occurs in both adults and children.

Hairy cell leukemia is a rare type of chronic leukemia. This article does not deal with hairy cell leukemia or other rare types of leukemia.

Who is at risk?

No one knows the exact causes of leukemia. Doctors can seldom explain why one person gets this disease and another does not. However, research has shown that people with certain risk factors are more likely than others to develop leukemia. A risk factor is anything that increases a person's chance of developing a disease.

Studies have found the following risk factors for leukemia:

Very high levels of radiation. People exposed to very high levels of radiation are much more likely than others to develop leukemia. Very high levels of radiation have been caused by atomic bomb explosions (such as those in Japan during World War II) and nuclear power plant accidents (such as the Chernobyl [also called Chornobyl] accident in 1986).

Medical treatment that uses radiation can be another source of high-level exposure. Radiation used for diagnosis, however, exposes people to much lower levels of radiation and is not linked to leukemia.

Working with certain chemicals. Exposure to high levels of benzene in the workplace can cause leukemia. Benzene is used widely in the chemical industry. Formaldehyde is also used by the chemical industry. Workers exposed to formaldehyde also may be at greater risk of leukemia.

Chemotherapy. Cancer patients treated with certain cancer-fighting drugs sometimes later develop leukemia. For example, drugs known as alkylating agents are associated with the development of leukemia many years later.

Down's syndrome and certain other genetic diseases. Some diseases caused by abnormal chromosomes may increase the risk of leukemia.

Human T-cell leukemia virus-I (HTLV-I). This virus causes a rare type of chronic lymphocytic leukemia known as human T-cell leukemia. However, leukemia does not appear to be contagious.

Myelodysplastic syndrome. People with this blood disease are at increased risk of developing acute myeloid leukemia.

In the past, some studies suggested exposure to electromagnetic fields as another possible risk factor for leukemia. Electromagnetic fields are a type of low-energy radiation that comes from power lines and electric appliances. However, results from recent studies show that the evidence is weak for electromagnetic fields as a risk factor.

Most people who have known risk factors do not get leukemia. On the other hand, many who do get the disease have none of these risk factors. People who think they may be at risk of leukemia should discuss this concern with their doctor. The doctor may suggest ways to reduce the risk and can plan an appropriate schedule for checkups.

Symptoms

Like all blood cells, leukemia cells travel through the body. Depending on the number of abnormal cells and where these cells collect, patients with leukemia may have a number of symptoms.

Common symptoms of leukemia may include:

Fevers or night sweats

Frequent infections

Feeling weak or tired

Headache

Bleeding and bruising easily (bleeding gums, purplish patches in the skin, or tiny red spots under the skin)

Pain in the bones or joints

Swelling or discomfort in the abdomen (from an enlarged spleen)

Swollen lymph nodes, especially in the neck or armpit

Weight loss

Such symptoms are not sure signs of leukemia. An infection or another problem also could cause these symptoms. Anyone with these symptoms should see a doctor as soon as possible. Only a doctor can diagnose and treat the problem.

In the early stages of chronic leukemia, the leukemia cells function almost normally. Symptoms may not appear for a long time. Doctors often find chronic leukemia during a routine checkup – before there are any symptoms. When symptoms do appear, they generally are mild at first and get worse gradually.

In acute leukemia, symptoms appear and get worse quickly. People with this disease go to their doctor because they feel sick. Other symptoms of acute leukemia are vomiting, confusion, loss of muscle control, and seizures. Leukemia cells also can collect in the testicles and cause swelling. Also, some patients develop sores in the eyes or on the skin. Leukemia also can affect the digestive tract, kidneys, lungs, or other parts of the body.

Diagnosis

If a person has symptoms that suggest leukemia, the doctor may do a physical exam and ask about the patient's personal and family medical history. The doctor also may order laboratory tests, especially blood tests.

The exams and tests may include the following:

Physical exam. The doctor checks for swelling of the lymph nodes, spleen, and liver.

Blood tests. The lab checks the level of blood cells. Leukemia causes a very high level of white blood cells. It also causes low levels of platelets and hemoglobin, which is found inside red blood cells. The lab also may check the blood for signs that leukemia has affected the liver and kidneys.

Biopsy. The doctor removes some bone marrow from the hipbone or another large bone. A pathologist examines the sample under a microscope. The removal of tissue to look for cancer cells is called a biopsy. A biopsy is the only sure way to know whether leukemia cells are in the bone marrow.

There are two ways the doctor can obtain bone marrow. Some patients will have both procedures:

- Bone marrow aspiration: The doctor uses a needle to remove samples of bone marrow.
- Bone marrow biopsy: The doctor uses a very thick needle to remove a small piece of bone and bone marrow.

Local anesthesia helps to make the patient more comfortable.

Cytogenetics. The lab looks at the chromosomes of cells from samples of peripheral blood, bone marrow, or lymph nodes.

Lumbar puncture. The doctor removes some of the cerebrospinal fluid (the fluid that fills the spaces in and around the brain and spinal cord). The doctor uses a long, thin needle to remove fluid from the spinal column. The procedure takes about 30 minutes and is performed with local anesthesia. The patient must lie flat for several hours afterward to keep from getting a headache. The lab checks the fluid for leukemia cells or other signs of problems.

Chest X-ray. The X-ray can reveal signs of disease in the chest.