Leukemia

Leukemia is a cancer of the blood and develops in the bone marrow, the body tissue that produces blood cells. The bone marrow is a jelly-like substance that fills the inside of the bones.

The bone marrow makes three kinds of cells:

1. Red blood cells (erythrocytes): They give the blood its red color. These cells pick up oxygen and carry it to the tissues. They are also known as RBCs.

2. Platelets (thrombocytes): They help stop bleeding if there is injury.

3. White blood cells (leukocytes): They fight infections. They are also known as WBCs. Leukemia develops in these blood cells. In leukemia, certain white blood cells escape the normal control mechanisms that direct their maturing. Instead of aging so they are able to assume certain functions, they remain young and continue to multiply. This can happen to any of three main kinds of white blood cells:
   1. Neutrophils, which eat bacteria
   2. Lymphocytes, which make substances to fight bacteria
   3. Monocytes, which destroy foreign materials.
      

What Is a Blast?

In speaking about leukemia, "blast" is the short name used for lymphoblasts, the immature white blood cells. There are normal blasts and leukemic blasts. Normally, blasts compose less than 5 percent of the cells made by the bone marrow and grow to form mature white blood cells with certain typical features visible under the microscope. Leukemic blasts are abnormal because they remain immature and do not function like mature white blood cells. In many cases, they look different from normal blasts when viewed under a microscope.

What Happens In Leukemia?
When a large number of blasts (leukemic cells) appear in the bone marrow, several things happen. As the leukemic blast cells accumulate in the bone marrow, they begin to crowd out the normal blood cells that develop there. Eventually, they take up so much room that red blood cells, platelets, and normal white blood cells cannot be produced. When that happens, the young person develops symptoms indicating that normal blood cells are not being manufactured in adequate numbers:

• If red blood cells are crowded out by leukemic cells, the blood will look thin, which makes the patient look pale. The young person also may be tired, because the thin blood cannot carry enough oxygen to the heart, lungs, and muscles.

• If blood platelets are crowded out in the bone marrow, the young person may have bleeding problems and unusual bruising.

• If the normal, mature kind of white cells known as neutrophils are crowded out by the blasts, there will be no cells to combat bacteria, and infections may occur.

In some cases, leukemic blasts may spill over from the bone marrow into the blood, where they can be seen by microscopic examination. This may cause a rise in the number of white cells in the blood (the white blood cell count). In other cases, only a few blasts appear in the blood, and the white cell count does not change much. When leukemic blasts are present in the blood, they may be carried to other places in the body and enter various body organs. Sometimes they grow in these organs as well as in the bone marrow.

Kinds of Leukemia in Young People
Leukemia is not just one disease. There is actually a type of leukemia for each of the three major kinds of white blood cells-neutrophils, lymphocytes, and monocytes.

Leukemia in any one person can affect only one kind of blood cell. The most common kinds of leukemia are lymphocytic (also called lymphoblastic or lymphoid) and myelogenous (also called granulocytic, myelocytic, myeloblastic, or myeloid). Other types (monocytic, myelomonocytic, progranulocytic, or erythroleukemia) are very rare but still act much like the more common kinds.

If leukemia affects a young person quickly, it is called "acute" because it comes on suddenly and progresses rapidly without treatment. Almost all childhood leukemias are acute, but the disease is some times of the "chronic" type. In chronic leukemia, the bone marrow is able to produce a good number of normal cells as well as leukemic cells so that, compared to acute leukemia, the actual disease course is milder for a period of time. Even without treatment, the disease usually progresses more slowly.

Acute Lymphocytic Leukemia (ALL for short) is commonly known as "childhood leukemia." It is the most commonly occurring cancer in children. As its name suggests, it affects the lymphocytes. Most children are between 2 and 8 years old when diagnosed, but the disease can occur in people in their twenties and thirties as well. For reasons yet to be understood, slightly more boys get ALL than girls, and it occurs more frequently among white children than black children.

Acute Myelogenous Leukemia (AML) is also called acute granulocytic leukemia. It usually occurs in people over 25 but sometimes is found in teenagers and children. In AML, the leukemic blasts develop from the stem cells that would normally give rise to neutrophils. The characteristics of the blasts in AML are generally similar to those of acute lymphocytic leukemia, but special tests can be done to help determine whether a leukemia is myelogenous or lymphocytic.

Chronic Myelogenous Leukemia (CML) is not common in children. CML's distinguishing feature is the presence of very large numbers of immature neutrophil cells, which seem to mature more efficiently than blast cells. The progression of CML varies greatly, sometimes changing to a type of acute myelogenous leukemia.

Diagnosis and Treatment
Diagnosis of leukemia requires blood tests and examination of the cells in the bone marrow, because early symptoms can mimic many other diseases including mononucleosis, anemia arising from other causes, tonsillitis, rheumatic conditions, meningitis, mumps, and other kinds of cancer.

In any acute leukemia, it is necessary to determine which type of white blood cell has become leukemic, because treatment and response to it are different for each kind. Usually the type of leukemic cell involved can be determined from its appearance under the microscope, but sometimes special tests of the chromosomes and cell chemistry are needed for complete certainty. In rare instances, the cells are too young to be classified. Such cases are called acute stem cell leukemia or acute undifferentiated leukemia (AUL). Other tests such as x-rays and lumbar puncture may also be undertaken to determine if areas other than the bone marrow are involved.

The primary treatment for leukemia is combination chemotherapy, where two or more anticancer medications are used to control or eradicate the disease. Radiation, platelet and red cell transfusions, antibiotic therapy, and occasionally surgery (for unusual complications) are also a part of many treatment programs. In some forms of leukemia, bone marrow transplantation is done.

Information provided by the National Cancer Institute.

Each year, Medical College of Wisconsin physicians care for more than 180,000 patients, representing nearly 500,000 patient visits. Medical College physicians practice at Children's Hospital of Wisconsin, Froedtert Memorial Lutheran Hospital, the Milwaukee VA Medical Center, and many other hospitals and clinics in Milwaukee and southeastern Wisconsin.