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More About Leukemia

Leukemia: Introduction

What is cancer?

Cancer is when cells in the body change and grow out of control. Your body is made up of tiny building blocks called cells. Normal cells grow when your body needs them, and die when your body does not need them any longer. Cancer is made up of abnormal cells that grow even though your body doesn’t need them. In most types of cancers, the abnormal cells grow to form a lump or mass called a tumor.

Leukemia is different from most other cancers. Leukemia is cancer that starts in the bone marrow. The bone marrow is where new blood cells are made. It's a thick, spongy liquid inside your bones.

Leukemia starts in early forms of blood cells, usually white blood cells, which help fight infections. When you have leukemia, your body makes too many blood cells, and they aren’t normal. Leukemia cells do not usually form tumors. But they can travel in the blood and go all over the body. That means they can reach almost any organ. So leukemia can cause problems and be found in many different ways, depending on which organs are involved.

Anatomy of  a bone, showing blood cells

What are normal blood cells?

Blood is made up of liquid, called plasma, and 3 kinds of cells. Each kind of cell has a special task:

  1. White blood cells help the body fight infection and disease.

  2. Red blood cells carry oxygen from the lungs to the body's tissues and carry carbon dioxide from the tissues to the lungs.

  3. Platelets help form blood clots and control bleeding.

Blood cells are made in the soft center of the bones called the bone marrow. In adults, active bone marrow is found in the hip bones, ribs, spine, and skull. Normal cells in the bone marrow develop from very immature cells into mature, working cells ready to leave the bone marrow. Early, less mature, non-working forms of new blood cells are called blasts.

As cells mature in the bone marrow, they become smaller and more compact. They are better able to do their special jobs. Some new blood cells stay in the bone marrow to grow, while others move to other parts of the body to grow. Blood cells are produced at a higher rate when the body needs them, such as when a person has an infection or low numbers of red blood cells (anemia). This process helps the body stay healthy.

What are leukemia cells?

When a person has leukemia, the body makes too many blood cells of one type. These abnormal cells, usually white blood cells, don't mature and look different from normal blood cells. They don't work as they should. They also interfere with the making of other blood cells, usually red blood cells and platelets.

Types of leukemia

Two types of abnormal white blood cells can turn into leukemia: lymphoid cells and myeloid cells.

  • When leukemia involves the lymphoid cells, it is called lymphocytic or lymphoblastic leukemia. 

  • When it is found in the myeloid cells, it is called myelogenous or myeloid leukemia.

Leukemias are also grouped based on how fast they grow:

  • Acute leukemias get worse very quickly.

  • Chronic leukemias tend to be slow growing, but may get worse over time.

In acute leukemia, the abnormal blood cells are usually young cells (immature blasts) that do not work the way they should. These cells grow quickly. Acute leukemia quickly gets worse unless it is treated right away.

In chronic leukemia, young blood cells are present, but mature, functional cells are also made. In chronic leukemia, blasts grow slowly. It takes longer for the disease to get worse.

These categories result in 4 combinations, which make up the main types of leukemia:

  • Acute lymphoblastic leukemia (ALL). ALL is the most common type of leukemia in children. But it can occur in adults.

  • Acute myeloid leukemia (AML). AML is one of the most common types of acute leukemia in adults. It can also occur in children.

  • Chronic lymphocytic leukemia (CLL). CLL is also among the most common types of leukemia in adults. It is mostly seen in older adults. It may be seen in younger adults, but almost never in children.

  • Chronic myelogenous leukemia (CML). CML is a slightly less common type of leukemia that is seen mostly in adults. Very few children develop this type of leukemia. 

Leukemia: Risk Factors

Woman smoking a cigarette.

What is a risk factor?

A risk factor is anything that may increase your chance of having a disease. Risk factors for a certain type of cancer might include smoking, diet, family history, or many other things. The exact cause of someone’s cancer may not be known. But risk factors can make it more likely for a person to have cancer.

Things you should know about risk factors for cancer:

  • Risk factors can increase a person's risk, but they do not necessarily cause the disease.

  • Some people with one or more risk factors never develop cancer. Other people can develop cancer and have no risk factors.

  • Some risk factors are very well known. But there is ongoing research about risk factors for many types of cancer.

Some risk factors, such as family history, may not be in your control. But others may be things you can change. Knowing the risk factors can help you make choices that might lower your risk. For example, if smoking is a risk factor, you may choose to quit smoking.

Who is at risk for leukemia?

Anyone can get leukemia. In many people the cause of their leukemia is not known. But some risk factors for leukemia are known.


People who smoke are more likely to get acute myeloid leukemia (AML) than people who do not smoke.

Exposure to certain chemicals

Being exposed to certain chemicals has been linked with some types of leukemia. For example, exposure to benzene is a risk factor for AML. It may also be a risk factor for acute lymphocytic leukemia (ALL). Exposure to Agent Orange, an herbicide used in the Vietnam War, has been linked to an increased risk for chronic lymphocytic leukemia (CLL).

Chemotherapy in the past

People who get certain chemotherapy medicines to treat other cancers are more likely to get AML or ALL later on. A person's risk for leukemia is higher for a number of years after the first cancer is treated. But this small increased risk of getting leukemia later on does not outweigh the need to use these medicines to treat the cancer.

Radiation exposure

High doses of radiation raise a person's risk for AML, ALL, and chronic myeloid leukemia (CML). This exposure could be from an atomic bomb blast or a nuclear reactor accident, as well as from radiation therapy to treat another type of cancer.

Rare congenital diseases

A small number of people are at greater risk for AML and ALL because they have certain rare diseases from the time they are born. For example, people with Down syndrome, ataxia-telangiectasia, and Bloom syndrome have an increased risk of getting these acute forms of leukemia.

Certain blood disorders

People who have certain blood diseases are more likely to get AML. These diseases include myelodysplastic syndromes. 

Family history

Most people who get leukemia do not have a family history of it. But people with relatives who have AML or CLL may be at increased risk.


Most types of leukemia, especially chronic leukemias, become more common as people get older. But ALL is more common in children than in adults.


Most types of leukemia are slightly more common in males than in females. Doctors do not know why this is so. 

What are your risk factors?

Talk with your healthcare provider about your risk factors for leukemia and what you can do about them.