Leukemia is cancer of the blood cells. The disease develops when the body produces large numbers of abnormal blood cells, usually white blood cells, which look different from healthy cells and do not function properly. Leukemia starts in the bone marrow but can then spread to the blood, lymph nodes, spleen, liver, central nervous system and other organs.
How are blood cells supposed to work? What goes wrong in leukemia?
Blood is made up of fluid called plasma and three types of blood cells:
White blood cells help the body fight infections and other diseases. There are several different kinds of white blood cells, each with a specific role in warding off infections. The three main types are granulocytes, monocytes, and lymphocytes. (The suffix “-cyte” means cell.)
Red blood cells carry oxygen from the lungs to tissues throughout the body. They then transport carbon dioxide away from the tissues back to the lungs.
Platelets help the body to control bleeding by forming blood clots.
Blood cells are made in the bone marrow – the soft, spongy center of bones. Early, immature blood cells are called stem cells. In a healthy person, stem cells grow in a controlled, orderly manner, maturing into red blood cells, white blood cells and platelets, as the body needs them.
Leukemia results when the process of maturation from stem cell to white blood cell goes awry, producing a genetic change that disrupts the normal control of cell division. The affected cells become cancerous, multiplying rapidly without any order. Eventually, the cancerous (leukemic) cells take over the bone marrow, replacing the normal cells that make healthy blood cells. The leukemic cells may also spread to other organs, including the liver, spleen, lymph nodes, kidneys and brain.
What are the different types of leukemia?
Leukemia has many different types and subtypes. They are categorized by how fast they progress and which types of white blood cells are affected. Acute leukemias spread quickly; chronic leukemias spread more slowly. Lymphocytic leukemias affect lymphocytes; myeloid (also called myelogenous) leukemias affect either granulocytes or monocytes.
The four major forms of leukemia are:
- acute lymphocytic leukemia (ALL):
- acute myeloid leukemia (AML);
- chronic lymphocytic leukemia (CLL);
- chronic myeloid leukemia (CML).
Chronic leukemias predominantly affect adults. Acute leukemias occur in both adults and children. Acute lymphocytic leukemia is the most common type of leukemia in young children.
What causes leukemia?
The cause of leukemia in humans is unknown. However, viruses have been shown to cause some leukemias in animals, such as cats. In people, a virus called HTLV-1 (human T-cell lymphotropic virus type I) is strongly suspected to cause a rare type of leukemia, adult T-cell leukemia.
What are the risk factors associated with leukemia?
Exposure to radiation and certain chemicals, such as benzene, is associated with an increased risk of developing leukemia. So, too, is the use of some chemotherapy drugs used to treat certain cancers. In addition, people who have certain genetic disorders, such as Down syndrome and Fanconi’s syndrome, are more likely to get leukemia. As with all cancers, smoking is also a known risk factor.
What are the symptoms of leukemia?
When the bone marrow fails to produce enough normal blood cells, various symptoms arise. Because people with leukemia have too few healthy white blood cells to fend off infections, they tend to get repeated infections and fevers. Leukemia sufferers also have fewer than the normal number of healthy red blood cells, which means there are not enough red blood cells to carry oxygen to cells throughout the body. This condition is called anemia and causes patients to look pale as well as to feel weak and fatigued. Leukemia can also result in too few healthy platelets, which are responsible for blood clotting. This makes patients bruise and bleed easily, often in the form of nosebleeds, bleeding gums, and purple skin blotches.
In acute leukemia, symptoms get worse quickly and people with the disease usually visit the doctor because of the symptoms.With chronic leukemia, however, symptoms may not appear for a long time and, when they do appear, they are usually mild and worsen gradually. For this reason, chronic leukemia is often found accidentally during a routine check-up, before any symptoms develop.
How is leukemia detected?
Routine blood tests, such as a complete blood count (CBC), are often the first indication that a person has leukemia. People with leukemia usually have too many white blood cells, too few red blood cells, and too few platelets. In addition, very immature white blood cells called blasts are observed in blood samples when examined under a microscope. Blasts are not normally found in circulating blood, and they do not work the way mature cells do. Their presence alone is strong enough evidence to diagnose leukemia.
Bone marrow aspiration or a bone marrow biopsy is almost always done to confirm a diagnosis of leukemia and to determine the type. In bone marrow aspiration, a thin needle is inserted into a large bone (usually the hip) and is used to draw out a small sample of liquid bone marrow. In a bone marrow biopsy, a larger needle is used to remove a small cylinder of bone and bone marrow.
If leukemic cells are found in the bone marrow sample, the doctor will order several laboratory tests to find out how far the disease has progressed. The series of tests may include a spinal tap (lumbar puncture), in which a needle is inserted into the spinal cavity in the lower back to draw out a sample of cerebrospinal fluid – the fluid that fills the spaces in and around the brain and spinal cord. The fluid sample is examined for leukemic cells. Imaging tests, such as x-rays, may also be ordered to check for signs of leukemia in other organs.
How is leukemia classified?
Although most cancers are classified in stages that define the size of the tumor and how far the cancer has spread, this staging system is not used for leukemia. The reason is that leukemia does not usually form a mass or tumor. Rather, it affects all the bone marrow and often has already spread to other organs.
Leukemias are classified based on the results of lab tests that define several features of the disease, such as the number of white blood cells in the blood and bone marrow, the presence or absence of anemia, the platelet count, and the size of the spleen (a blood-forming organ in early life and later a storage organ for red blood cells and platelets). The doctor uses these features to guide the patient’s treatment plan.
How is leukemia treated?
Most patients with leukemia are treated with chemotherapy. Some also have stem cell transplantation or interferon therapy.
Chemotherapy (the use of cancer-killing drugs that enter the bloodstream and travel throughout the body) is the mainstay of leukemia treatment. It usually involves a combination of several anticancer drugs given over a period of time, often in cycles, but the specific treatment schedule depends on the type of leukemia a patient has. Because treatment destroys bone marrow cells, the patient may need to have red blood cells transfusions to treat anemia, platelet transfusions to control bleeding, and powerful antibiotics to treat or prevent infections.
In addition to the usual side effects associated with chemotherapy, such as temporary hair loss, nausea, vomiting, and loss of appetite, a condition called tumor lysis syndrome may result from the destruction of leukemia cells. When leukemic cells die, they release substances into the bloodstream that can harm the kidneys, the heart and the nervous system. Fortunately, tumor lysis syndrome, which is more common in people with acute leukemia than in people with chronic leukemia, can be prevented by giving the patient extra fluids or certain drugs that help the body to cleanse itself of toxins.
Stem cell transplantation provides doctors with a way to use very high doses of chemotherapy for more effective treatment. This complex therapy involves harvesting stem cells (primitive blood cells) from the bone marrow or the blood stream in a process called apheresis. The stem cells can be collected from the patient or a suitable donor. (For people with acute leukemia, the cells are usually taken from a donor, as it can be difficult to find cancer-free cells in the patient’s own marrow.) The patient is then given extremely high doses of chemotherapy and may also get total body radiation to kill any remaining cancer cells. Afterward, the stored stem cells are given to the patient as a blood transfusion. If successful, it takes about two to three weeks after the stem cells are infused for the cells to start making new white blood cells. They then start making platelets, followed by red blood cells.
Interferon therapy is another treatment option for some types of leukemia. Interferons are natural substances produced by the body and can help the immune system to normalize the bone marrow by slowing the growth of leukemic cells. Interferon therapy is usually administered as a shot given once a day. Side effects include bone pain, muscle aches, headaches, fatigue, cloudy thinking, and nausea. There are drugs, however, that can ease these side effects during therapy.
- Weight loss
- Repeated infections
- Bruising easily
- Excessive exposure to ionizingradiation and to benzene
- Blood test
- Bone marrow biopsy
- Blood transfusions
- Bone marrow transplantation
- Clinical trials
- Avoid exposure to environmental pollutants
- Maximize protection against pollutants