Acute Lymphocytic Leukemia - Prognosis

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Ploidy. Ploidy refers to the number of chromosomes. Additional copies (hyperdiploidy) or absence of copies (hypodiploidy) of chromosomes affect prognosis. For example, in children hyperdiploidy is associated with a more favorable outcome and hypodiploidy with a poorer outcome. (Hypodiploidy occurs in only 1% of children with ALL.)

Morphology

The morphology of a cell includes its physical characteristics, such as shape and structure. To determine the morphology of the leukemia cells, samples of the bone marrow are taken and particular contents of the cells are stained with a dye. They are then examined under a microscope.

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Acute lymphocytic leukemia cells are grouped, according to the French-American-British (FAB) classification system, into three ALL morphologic types. (It should be noted that this system is subjective and is now used to complement other diagnostic tests mentioned above):

• L1 cells. These are small blasts with scant amounts of cytoplasm (the substance in a cell between its membrane and nucleus). L1 cells usually contain a round nucleus and there is little variation among them. L1 represents the most common ALL morphology and offers the best prognosis. It occurs in about 85% of children and 30% of adults with ALL.
• L2 cells. These cells are larger than L1 and have more abundant cytoplasm. They vary significantly among each other and have an irregularly shaped nucleus. L2 morphology conveys a poorer prognosis than L1, although the two cells' types are treated similarly. Subtype L2 is the most common morphologic type in ALL adults; 64% of adults with ALL have this subtype compared with only 15% of children.
• L3 cells. These are uncommon. They resemble another malignancy called Burkitt's lymphoma, and their treatments are now the same.

Determination of Minimal Residual Disease

Assays that test for cancerous cells are improving, allowing doctors to detect smaller and smaller amounts of hidden disease. For example, flow cytometry assays can detect 0.01% leukemic cells, and PCR assays can detect 0.001% leukemic cells. A new concept called minimal residual disease (MRD) is becoming an important prognostic factor in ALL. A more precise measure of disease response, MRD may soon replace existing measures such as "complete response" and "partial response" when assessing the effectiveness of ALL treatment. Ongoing studies of MRD in ALL may help identify patients in remission who are at risk of relapse. In addition, early therapeutic intervention based on the presence of MRD may improve outcome and prolong survival.

Drawing Conclusions from Cell Characteristics

Using the results of the tests described above, patients are classified into low-, average-, and high-risk groups. This information allows the doctor to diagnosis the type of leukemia and plan the best treatment. Each classification requires unique therapies.

Doctors attempt to make a prognosis and determine an optimal treatment plan by assessing all the cell characteristics plus the white blood cell count. As examples:

• Patients who have an L1 or L2 morphology, a white blood cell count of less than 15,000 mm3, a t(12;21) genetic translocation, and a cALLa-positive antigen marker have an excellent outlook.
• On the other hand, patients who have an L2 morphology, a white blood cell count greater than 30,000 mm3, and who lack the cALLa marker have a poorer prognosis and require more aggressive treatment.

Review Date: 01/16/2007
Reviewed By: Harvey Simon, MD, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital

A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org).