Acute Lymphocytic Leukemia (ALL)

Acute Lymphocytic Leukemia (ALL)

Acute lymphocytic leukemia occurs when an early form of a white blood cell in the bone marrow suffers a genetic defect. The cell multiples continuously and fails to mature properly. The resulting abnormal cells, which are called lymphoblasts or leukemic blasts, do not function properly. They also build up in the bone marrow, crowding out other types of blood cells. The result is a shortage of red blood cells, platelets, and healthy white blood cells. Such shortages cause anemia, bleeding and bruising, and a diminished ability to fight infections.

Symptoms

Many people who develop ALL feel fatigued, achy, or just "not well." They may feel short of breath and may notice unusual bruising or bleeding, tiny red marks under the skin, or joint or bone pain. They also commonly develop infections. Most of these symptoms are caused by a lack of healthy blood cells of all types.

In some cases, leukemic cells collect in the central nervous system, causing headaches and vomiting. They can also collect in the lymphatic system, causing enlarged lymph nodes. Cells may invade the spleen and liver, leading to swelling and tenderness. Enlarged lymph nodes may put pressure on nearby structures such as the windpipe, causing shortness of breath. They can also put pressure on a large vein that passes near the thymus, causing the head and arms to swell. This condition is known as superior vena cava syndrome.

Most people have symptoms for only a few weeks before leukemia is diagnosed. Sometimes the onset of symptoms is so dramatic that diagnosis is sought after only a few days.

Who Gets ALL

Acute lymphocytic leukemia is the most common type of leukemia diagnosed in children, accounting for 85% of all cases of childhood leukemia.

ALL also occurs in adults.

Risk Factors

It is rarely possible to say exactly what caused one person's leukemia. Scientists do know, however, that one risk factor for ALL is very high doses of radiation. They also think that ALL in some children might be caused by exposure to an infectious or toxic agent of some kind while the child was in the womb or very young.

Subtypes of ALL

Within the diagnosis of ALL are several different subtypes of disease. Knowing which subtype is present can help in predicting the course of the disease and in selecting the best therapy.

Three primary subtypes are defined by the size and shape of the leukemic cells as seen under a microscope.

• L1 subtype cells are small and more mature than the other types. It is the most common subtype found in children, and also occurs in 30 percent of the adults who have ALL.

• L2 subtype cells are larger, but more immature, and the nuclei vary in shape. It occurs in 65 percent of adult cases.

• L3 subtype cells are large and the nuclei seem to all have the same shape. It is the least common subtype, and is found in only 5 percent of adult cases. It is also called Burkitt's type leukemia.

Leukemia cells can also be classified by their immunophenotypes, or which cell line they developed from. This is done by looking at certain characteristic markers on the surface of the cells to see which type of normal lymphocytes the cells resemble. There are three subtypes in this category.

• Precursor B-cell subtype -- the most common subtype in both children and adults
• T-cell subtype
• B-cell subtype (also known as L3, or Burkitt's type)

Another important characteristic of ALL is whether certain chromosomal changes are present. A common abnormality is the Philadelphia chromosome, in which a portion of the genetic material on one chromosome has been swapped with material from another chromosome. This exchange of material is called a translocation. In this case, chromosome 22 is exchanging material with chromosome 9. The altered genetic material now found on chromosome 22 is called the BCR-ABL fusion gene. It tells the body to produce a protein that somehow triggers the growth of leukemia cells. The Philadelphia chromosome is found in more than 30 percent of adults with ALL, and usually indicates a poorer prognosis and the need for more aggressive treatment. It is less common in children.

Prognostic Factors

In adults, the single most important prognostic indicator is age. Treatment results are best in young adults. Patients over the age of 60 have lower responses to remission induction therapy and more severe side effects from treatment.

In children, certain characteristics of ALL and the patients themselves are known to confer a better prognosis. Based on these factors, patients may be termed low-risk or high-risk. Those who are considered high-risk may receive more aggressive treatment.

In adults, patients with the best prognosis are those who have an initial leukocyte count of under 50,000/mm³, are diagnosed with the L1 or L2 subtype or the T-cell subtype, do not have the Philadelphia chromosome, or have achieved a remission in less than five weeks.

Note that these prognostic factors were developed by looking at large groups of patients; they do not necessarily predict the outcome for any single patient.