ZAP-70 Methylation May be Easier to Test for than ZAP-70 Protein

April 5, 2006

ZAP 70 methylation: a new prognostic marker in CLL

Oscier, M.D.

Royal Bournemouth Hospital (United Kingdom)

Abstract:

Most patients with chronic lymphocytic leukemia (CLL) are

asymptomatic at diagnosis and wish to know the likely natural history

of their disorder. ZAP70 is signaling molecule essential for the

function of a subset of normal white blood cells (T lymphocytes). It

is also expressed in the leukemic cells of a subset of patients with

CLL and correlates with a shorter time from diagnosis to first

treatment and with shorter survival.

There is increasing evidence that ZAP 70 expression contributes to

the poorer prognosis of ZAP70 positive cases and is not simply a

marker of aggressive disease. Recent data suggest that ZAP 70 may

also be a target for therapy.

Most laboratories measuring ZAP70 expression use a flow cytometric

assay, which is widely available, rapid and inexpensive.

Unfortunately this assay is not standardized such that a sample may

be considered positive for ZAP 70 in one laboratory and negative in

another.

We have shown that a modification of the ZAP70 gene (DNA methylation)

correlates closely with ZAP70 expression measured by flow cytometry.

The methylation assay is not subject to many of the factors such as

sample age, which can affect the flow cytometric assay. However, the

methylation assay we have used so far is only semi quantitative and

gives an equivocal result in about 6% of cases.

We propose to use a rapid, sensitive and fully quantitative method

(Pyrosequencing) for detecting ZAP70 methylation. The prognostic

value of this assay will then be tested retrospectively in a cohort

of 300 patients with prolonged follow up, managed at a single center,

and prospectively in 300 patients entered into the UK CLL4 randomised

trial for previously untreated patients. Multivariate analysis will

be employed to determine whether ZAP 70 methylation provides

additional information to known prognostic factors.

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