Multicenter study of ZAP-70 expression in patients with B-cell chronic lymphocytic leukemia using an optimized flow cytometry method.

International audienceBACKGROUND: Flow cytometry allows specific assessment of the expression of ZAP-70, a promising new prognostic factor in B-cell chronic lymphocytic leukemia (B-CLL), but suffers from a lack of multicenter standardization. DESIGN AND METHODS: An optimized method for direct detection of ZAP-70 in flow cytometry was tested in a multicenter fashion. Adapted for frozen cells, this method includes a normalization step by addition of B cells from a pool of peripheral blood mononuclear cells collected from normal donors. ZAP-70 expression levels were assessed for 153 patients with typical B-cell chronic lymphocytic leukemia chronic lymphocytic leukemia. Results were expressed as the ratio of ZAP-70 mean fluorescence intensity between B-CLL cells and normal B cells. RESULTS: The statistically optimized cut-off of ZAP-70 positivity was a ratio of 1.4. Concordance between ZAP-70 and CD38 expression was 67%. Concordance between the mutational status of IgVH genes and ZAP-70 or CD38 expression was 87% and 65%, respectively. ZAP-70 was significantly expressed in 28%, 54% and 61% of patients with Binet stages A, B and C B-cell chronic lymphocytic leukemia, respectively (p=0.008). The absence of ZAP-70 expression was associated with isolated del(13q14), a cytogenetic abnormality with a good prognosis, while most patients with the del(17p13) poor prognosis cytogenetic marker expressed ZAP-70 (p