Leukemia is a type of blood cancer that involves the overproduction of abnormal white blood cells (leukocytes) in the bone marrow. As leukemia progresses, cancer cells crowd out healthy blood cells and cause symptoms of leukemia. Leukemia is very similar to other types of blood cancer, including lymphoma, myeloma, myeloproliferative neoplasms (MPNs), and myelodysplastic syndromes (MDS).

Like other cancers, leukemia is caused by genetic mutations that allow cells to divide and grow in a disorganized way. There are two main types of mutations, inherited and acquired.

Acquired mutations:

• Happen over the course of a person’s life
• Are caused by normal aging and exposure to carcinogens, such as radiation, certain chemicals, smoking, and some viruses
• Are present in the DNA of some cells

Inherited mutations:

• Are passed down from parents to children
• Are present in the DNA of all cells at birth
• Occur far less commonly

Most cancer is caused by acquired mutations. The cause of the mutation is usually unknown. It is uncommon for leukemia to run in families, and in most cases of leukemia there is no family history of blood cancer. However, there are some cases of inherited genetic conditions raising the risk for developing leukemia. It is still unclear why some people develop leukemia and others do not.

How Cells Transform Into Cancer

Normal cells divide in a regular, ordered fashion, forming new cells that are exact copies to replace old ones. Certain genes in each cell are responsible for telling cells when to divide and when to stop dividing. Other genes identify and fix problems in DNA that are copied incorrectly or cause cells with bad DNA to self-destruct rather than keep multiplying. If a genetic mutation causes one or more of these genes to turn off in some cells, the cells can divide at a faster rate without regulation or order, becoming more and more mutated. Mutations may accumulate, further speeding the unchecked growth of abnormal cells. When these disordered cells begin to invade nearby tissues or break off and migrate to other locations, they have become cancerous.

Risk Factors for Leukemia

It is important to note that while science is good at finding correlations — or apparent relationships — between factors and disease, correlation does not prove the factor causes the disease. Many risk factors for leukemia have been identified and are being studied for their role in the development of the disease.

Since genetic mutations cause leukemia, risk factors for leukemia include anything that can encourage mutations. It is also important to note that risk factors vary by the type of leukemia.

Age

Mutations in DNA are inevitable, and they accumulate with age. Researchers theorize that for cells in rapidly dividing tissues, such as blood stem cells, tens of thousands of mutations will likely accumulate by age 60. However, cancer only develops in a small percentage of people.

For most types of leukemia, risk increases with age. The median age is 65 for people diagnosed with acute myeloid leukemia (AML), chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL), and chronic myeloid leukemia (CML).

The exception to this rule is acute lymphocytic leukemia (ALL), which is typically diagnosed in people under age 20. The median age at which people are diagnosed with ALL is 15.

Inherited Factors

It is uncommon for leukemia to be an inherited disease. In most cases of leukemia, there is no family history of the condition. However, some inherited factors and familial genetic disorders can result in a higher risk for developing leukemia, especially childhood leukemia.

Having a brother or sister with leukemia slightly raises a child’s risk of developing acute leukemia. However, even among identical twins, the chance of the second twin developing childhood leukemia is only 1 in 5.

Genetic Disorders That Raise the Risk of Leukemia

Certain genetic disorders can increase the risk for developing childhood leukemia. Examples include:

• Li-Fraumeni syndrome
• Down syndrome (also known as trisomy 21)
• Neurofibromatosis
• Fanconi anemia

Some inherited conditions that affect the immune system can also raise the risk for developing leukemia. These include:

• Wiskott-Aldrich syndrome
• Bloom syndrome
• Shwachman-Diamond syndrome
• Ataxia-telangiectasia

Sex and Ethnicity

Overall, leukemia occurs most frequently in non-Hispanic people of European ancestry. Leukemia occurs more often in men — there are 33 percent more men living with leukemia than women, and more men die of leukemia. Leukemia is seen least frequently in people of Asian, Pacific Islander, Native American, and Native Alaskan backgrounds. Certain types of leukemia occur more commonly in certain ethnicities.

• ALL is more common in people with European ancestry or Hispanic ethnicity.
• AML is more common in men than women.
• CLL/SLL is more common in men and especially in men of European ancestry.
• Childhood leukemia (occurring before age 20) is most common in those of Hispanic ethnicity.

Environmental Factors

Anything that raises the risk for acquired genetic mutations also raises the risk for developing leukemia and other types of cancer. Several carcinogens have been identified as contributing to the risk for leukemia.

Radiation

High doses of radiation, including radiation therapy used to treat previous cancers, may lead to the development of leukemia in some people. Prolonged exposure to electromagnetic fields, such as experienced by those living near power lines, may raise the risk for developing ALL.

Chemicals

Frequent exposure to high levels of the chemical benzene is a possible cause of AML. Common sources of benzene exposure include tobacco smoking and secondhand tobacco smoke, exhaust from automobiles, and industrial pollution. Past treatment for other types of cancer with certain chemotherapy drugs can also raise the risk for developing leukemia.

Obesity

Research shows that obesity is associated with a 19 percent increased risk of developing leukemia in general. Obesity increases the risk for different types of leukemia to varying degrees:

• Acute lymphocytic leukemia (ALL) — 62 percent increased risk
• Acute myeloid leukemia (AML) — 38 percent increased risk
• Chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) — 17 percent increased risk
• Chronic myeloid leukemia (CML) — 27 percent increased risk

Acquired Mutations Associated With Leukemia

Scientists have identified many acquired genetic mutations in blood stem cells that play a role in the development of leukemia. Genetic testing of leukemic cells is often part of the leukemia diagnostic process, since it helps doctors distinguish between types of leukemia. Knowing which mutations are present in cancer cells helps doctors recommend effective treatment options. Read more about specific genetic mutations commonly associated with different types of leukemia.

Can Leukemia Be Prevented?

There is no certain way to avoid developing leukemia, especially in children. Most people who develop leukemia have no known risk factors. Most risk factors, including age, genetic predisposition, and ethnicity, are beyond anyone’s control. If you are concerned that you may have a high risk for developing leukemia, focus on lowering your risk by changing the environmental factors within your control.

• Stop smoking and avoid exposure to secondhand tobacco smoke.
• If you work with radiation or carcinogenic chemicals, take every precaution to limit your exposure. Use protective equipment and follow safety procedures consistently.
• General guidelines for cancer prevention recommend eating a healthy diet with plenty of fresh fruits, vegetables, and whole grains, and limiting your intake of red meat and processed meats. A balanced, nutritious diet can also encourage a healthy weight.

If your doctor has told you that you have risk factors for developing leukemia, make sure to attend all follow-up appointments to receive monitoring tests. You may not notice symptoms on your own. Diagnosing cancer early may mean there are more options for treatment.

Leukemia Condition Guide

• Leukemia — An Overview
• Types of Leukemia
• Symptoms of Leukemia
• Treatments for Leukemia
• Leukemia — The Path to Diagnosis
• Conditions Related to Leukemia