Leukemia is a cancer of the blood or bone marrow. Bone marrow produces blood cells. Leukemia can develop due to a problem with blood cell production. It usually affects the leukocytes, or white blood cells.
Leukemia is most likely to affect people over the age of 55 years, but it is also the most common cancer in those aged under 15 years.
The National Cancer Institute estimates that 61,780 people will receive a diagnosis of leukemia in 2019. They also predict that leukemia will cause 22,840 deaths in the same year.
Acute leukemia develops quickly and worsens rapidly, but chronic leukemia gets worse over time. There are several different types of leukemia, and the best course of treatment and a person's chance of survival depends on which type they have.
Leukemia develops when the DNA of developing blood cells, mainly white cells, incurs damage. This causes the blood cells to grow and divide uncontrollably.
Healthy blood cells die, and new cells replace them. These develop in the bone marrow.
The abnormal blood cells do not die at a natural point in their life cycle. Instead, they build up and occupy more space.
As the bone marrow produces more cancer cells, they begin to overcrowd the blood, preventing the healthy white blood cells from growing and functioning normally.
Eventually, the cancerous cells outnumber healthy cells in the blood.
There is a range of risk factors for leukemia. Some of these risk factors have more significant links to leukemia than others:
Artificial ionizing radiation: This could include having received radiation therapy for a previous cancer, although this is a more significant risk factor for some types than others.
Certain viruses: The human T-lymphotropic virus (HTLV-1) has links to leukemia.
Chemotherapy: People who received chemotherapy treatment for a previous cancer have a higher chance of developing leukemia later in life.
Exposure to benzene: This is a solvent that manufacturers use in some cleaning chemicals and hair dyes.
Some genetic conditions: Children with Down syndrome have a third copy of chromosome 21. This increases their risk of acute myeloid or acute lymphocytic leukemia to 2–3%, which is higher than in children without this syndrome.
Another genetic condition with links to leukemia is Li-Fraumeni syndrome. This causes a change to the TP53 gene.
Family history: Having siblings with leukemia can lead to a low but significant risk of leukemia. If a person has an identical twin with leukemia, they have a 1 in 5 chance of having the cancer themselves.
Inherited problems with the immune system: Certain inherited immune conditions increase the risk of both severe infections and leukemia. These include:
- ataxia-telangiectasia
- Bloom syndrome
- Schwachman-Diamond syndrome
- Wiskott-Aldrich syndrome
Immune suppression: Childhood leukemia may develop due to the deliberate suppression of the immune system. This might occur following an organ transplant as a child takes medications to prevent their body from rejecting the organ.
Several risk factors need further studies to confirm their link to leukemia, such as:
- exposure to electromagnetic fields
- exposure to certain chemicals in the workplace, such as gasoline, diesel, and pesticides
- smoking
- using hair dyes
There are four main categories of leukemia:
- acute
- chronic
- lymphocytic
- myelogenous
Chronic and acute leukemias
During its lifespan, a white blood cell goes through several stages.
In acute leukemia, developing cells multiply quickly and collect in the marrow and blood. They exit the bone marrow too early and are not functional.
Chronic leukemia progresses more slowly. It allows for the production of more mature, useful cells.
Acute leukemia overcrowds the healthy blood cells more quickly than chronic leukemia.
Lymphocytic and myelogenous leukemias
Doctors classify leukemia according to the type of blood cell they affect.
Lymphocytic leukemia occurs if cancerous changes affect the type of bone marrow that makes lymphocytes. A lymphocyte is a white blood cell that plays a role in the immune system.
Myelogenous leukemia happens when the changes affect bone marrow cells that produce blood cells, rather than the blood cells themselves.
Acute lymphocytic leukemia
Children under 5 years old are at the highest risk of developing acute lymphoblastic leukemia (ALL). However, It can also affect adults, typically over the age of 50 years. Out of every five deaths from ALL, four occur in adults.
Chronic lymphocytic leukemia
This is most common among adults over 55 years, but younger adults can also develop it. About 25% of adults with leukemia have chronic lymphocytic leukemia (CLL). It is more common in men than in women and rarely affects children.
Acute myelogenous leukemia
Acute myelogenous leukemia (AML) is more common in adults than in children, but overall, it is a rare cancer. It develops more often in men than in women.
It develops quickly, and symptoms include fever, difficulty breathing, and pain in the joints. Environmental factors can trigger this type.
Chronic myeloid leukemia
Chronic myelogenous leukemia (CML) mostly develops in adults. About 15% of all leukemia cases in the United States are CML. Children rarely develop this type of leukemia.
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