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Leukemia Introduction

People with leukemia now have more treatment choices and more hope for survival than ever before. Doctors keep finding new treatments for leukemia and ways to help people with leukemia have better lives. We are continually learning more about leukemia, including its prevention, detection, and treatment.

What is leukemia?

Leukemia is cancer that affects the bone marrow where blood cells are produced.

What are normal blood cells?

Blood is made up of liquid, called plasma, and three 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 composition
Click to enlarge

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 cells ready to leave the bone marrow. Early, less mature forms of new blood cells are called blasts.

anatomy of the long bones
Anatomy of the Long Bones: Yellow marrow can still produce blood cells when needed.

As cells mature in the bone marrow, they become smaller and more compact, and are better able to perform their special jobs. Some new blood cells remain 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 anemia. This process helps the body stay healthy.

What are leukemic cells?

When a person has leukemia, the body produces too many blood cells of one type. These abnormal cells, usually white blood cells, look different than normal blood cells and do not function correctly. They also interfere with 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.

Leukemia is grouped in two ways:

  1. Acute or chronic (depending on how fast the cells grow)

  2. Lymphoid or myeloid (depending on the type of white blood cell that has turned into leukemia)

In acute leukemia, the abnormal blood cells are usually immature blasts (young cells) that do not function properly. These cells grow quickly. Acute leukemia quickly gets worse unless it is treated immediately.

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

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

  • Acute lymphoblastic leukemia (ALL). ALL is the most common type of leukemia in children. But about one-third of cases of ALL occur in adults.

  • Acute myeloid leukemia (AML). AML is one of the most common types of acute leukemia in adults. AML can also occur in children, where it accounts for about one out of four leukemias.

  • Chronic lymphocytic leukemia (CLL). CLL is also among the most common types of leukemia in adults. It is mostly seen in older adults. It is sometimes 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.


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