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ZAP-70

ZAP-70

Test Highlight

ZAP-70

  

Clinical Use

  • Assess prognosis and need for aggressive therapy in patients with chronic lymphocytic leukemia (CLL)

Clinical Background

CLL has a highly variable course. Some patients survive for decades without needing treatment, whereas others progress rapidly and require aggressive therapy within several years after diagnosis. Predicting which patients will progress rapidly can help determine the need for close follow-up and may hold potential for risk-adapted treatment strategies.

The most established predictor of disease progression is lack of mutation in the immunoglobulin heavy chain variable region (IgVH) in neoplastic cells. However, because IgVH mutation testing is not widely available, several surrogate markers have been investigated. To date, the most effective such marker is expression of zeta-associated protein 70 (ZAP-70), a 70-kD member of the Syk family of protein tyrosine kinases. ZAP-70 is expressed primarily in T-cells and natural killer (NK) cells and is critical for signal transduction following T-cell receptor engagement. In CLL B-cells, elevated ZAP-70 expression appears to predict the need for therapy as effectively as IgVH mutation status. Although ZAP-70 expression is strongly correlated with IgVH mutation status, the combination of the 2 markers may provide greater prognostic value than either marker alone.

Method

This 4-color flow cytometry assay utilizes ZAP-70, CD3, CD19, and CD45 monoclonal antibodies. The fluorescently labeled lymphocyte population is selected by CD45 versus side scatter gating. The percentages of CD3 (B-cell)-positive and CD19 (T-cell)-positive lymphocytes expressing ZAP-70 are reported; samples in which 10% of the B-cell population expresses ZAP-70 are considered positive.

Interpretive Information

Positive ZAP-70 results predict an aggressive disease course. Patients with positive results require close follow-up to detect changes in clinical status. Negative results predict a more indolent disease course.

Testing for IgVH mutation status, available through Quest Diagnostics, may provide additional prognostic information.

 

This test was developed and its performance characteristics have been determined by Quest Diagnostics Nichols Institute. It has not been cleared or approved by the U.S. Food and Drug Administration. The FDA has determined that such clearance or approval is not necessary. Performance characteristics refer to the analytical performance of the test.

Content reviewed 12/2012

 
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