10% or 15% Might be Breakpoint for ZAP-70 Positivity

[Guest guest]

[Obviously, some differences of opinion as to what constitutes a

positive ZAP-70 level.]

Cytometry B Clin Cytom. 2006 Aug 11;70B(4):270-275 [Epub ahead of

print]

Variations in the detection of ZAP-70 in chronic lymphocytic

leukemia: Comparison with IgV(H) mutation analysis.

Sheikholeslami MR, Jilani I, Keating M, Uyeji J, Chen K, Kantarjian

H, O'brien S, Giles F, Albitar M.

Quest Diagnostics, Nichols Institute, San Capistrano, California.

Lack of immunoglobulin heavy chain genes (IgV(H)) mutation in

patients with chronic lymphocytic leukemia (CLL) is associated with

rapid disease progression and shorter survival. The zeta-chain (T-

cell receptor) associated protein kinase 70 kDa (ZAP-70) has been

reported to be a surrogate marker for IgV(H) mutation status, and its

expression in leukemic cells correlates with unmutated IgV(H).

However, ZAP-70 detection by flow cytometry varies significantly

dependant on the antibodies used, the method of performing the assay,

and the condition of the cells in the specimen. The clinical value of

ZAP-70 testing when samples are shipped under poorly controlled

conditions is not known. Furthermore, testing in a research

environment may differ from testing in a routine clinical laboratory.

We validated an assay for ZAP-70 by comparing results with clinical

outcome and the mutation status of the IgV(H). Using stored samples,

we show significant correlation between ZAP-70 expression and

clinical outcome as well as IgV(H) mutation at a cut-off point of

15%.

While positive samples (>15% positivity) remain positive when kept in

the laboratory environment for 48 hours after initial testing,

results obtained from samples from CLL patients tested after shipping

at room temperature for routine testing showed no correlation with IgV

(H) mutation status when 15% cut-off was used. In these samples, cut-

point of 10% correlated with the IgV(H) mutation (P = 0.0001). This

data suggests that although ZAP-70 positivity correlates with IgV(H)

mutation status and survival, variations in sample handling and

preparation may influence results.

We show that IgV(H) mutation results, unlike ZAP-70 remain correlated

with CD38 expression and beta-2 microglobulin in shipped samples, and

ZAP-70 testing should not be used as the sole criterion for

stratifying patients for therapy.

© 2006 International Society for Analytical Cytology.

PMID: 16906585 [PubMed - as supplied by publisher]