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

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 (IgV_H) in neoplastic cells. However, because IgV_H 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 IgV_H mutation status. Although ZAP-70 expression is strongly correlated with IgV_H mutation status, the combination of the 2 markers may provide greater prognostic value than either marker alone.

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.

CPT codes*: 88184, 88185, 88187

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 IgV_H mutation status, available through Quest Diagnostics, may provide additional prognostic information.

Submit 5 mL room-temperature EDTA (lavender-top tube) whole blood (1 mL minimum). Green-top and yellow-top tubes are also acceptable.

Alternatively, submit 5 mL bone marrow in EDTA or heparin (1 mL minimum).

Samples must be assayed within 3 days of collection.