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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. Leukemia cells are early forms of blood cells. They are usually white blood cells, which normally help fight infections. When your 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 with the blood all over the body. That means they can reach almost any organ. So leukemia can be present in many different ways, depending on which organs are involved.

Anatomy of  a bone, showing blood cells
Click Image to Enlarge

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

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 leukemia cells?

When a person has leukemia, the body makes too many blood cells of one type. These abnormal cells, usually white blood cells, 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.

#TomorrowsDiscoveries: DNA Rearrangements That Cause Childhood Cancer - Dr. Stephen

#TomorrowsDiscoveries: To battle invaders, our immune system deploys antibodies, made by shuffling bits of DNA. But if the DNA and developing immune cells are misshuffled, they can cause childhood cancer.

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. Lymphocytic or myeloid, depending on the type of white blood cell that has turned into leukemia

In acute leukemia, the abnormal blood cells are usually young cells (immature blasts) that do not work as they should properly. 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 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. In children, it makes up about 1 in 4 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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