Chronic Lymphocytic Leukemia (CLL) with Discordance in ZAP-70 Expression and IgVH Mutation Status.

In CLL patients, ZAP-70 expression is associated with an unmutated status of the variable immunoglobulin heavy chain gene (IgVH) region. Both features bear an adverse prognostic value. However, in various published series there is a proportion of cases with discordance in the expression of these two markers (i.e. ZAP-70-/IgVH unmutated or ZAP-70+/IgVH mutated) ranging from 5 to 30%. In order to clarify the outcome of this subgroup of patients, information on the clinico-biological features of the discordant cases is becoming increasingly more relevant. From November 2002 to April 2006, we evaluated ZAP-70 and CD38 expression, IgVH mutation status and cytogenetic aberrations by FISH in 125 young and untreated patients: 69 males, 56 females, with a median age of 51 years (range 29–64). According to Binet’s staging system, 81% were stage A, 15% stage B and 4% stage C. Eighty % of patients presented stable disease and 20% progressive disease. After a median follow-up of 40 months (range 3–191) from diagnosis, 32% of cases have required therapy. ZAP-70, evaluated by immunocytochemistry and flow-cytometry, was positive (≥7%) in 36% of cases, IgVH genes were unmutated (≥98% homology) in 25% and CD38 was positive (≥7%) in 18%. The correlations between ZAP-70/IgVH, CD38/IgVH and CD38/ZAP-70 were highly significant (p≤0.001 each) with a proportion of discordant cases of 21%, 16% and 24%, respectively. Focusing on 114 cases with available data for both ZAP-70 and IgVH mutation status, three groups were identified: 23 ZAP-70+/IgVH unmutated, 67 ZAP-70-/IgVH mutated, 24 discordant cases. Significant differences were found in terms of distribution of cytogenetic aberrations, CD38 expression and atypical lymphocyte morphology (Table I). Only 2 cases showed V3-21 usage: both were IgVH mutated, 1 was ZAP-70+ and the other ZAP-70-. Of the 24 discordant cases, 18 (75%) were ZAP-70+/IgVH mutated and 6 (25%) ZAP-70-/IgVH unmutated. No significant difference was shown between the two groups regarding the presence of poor risk genetic abnormalities del(17p), del(11q) and +12 (p=0.17), CD38 expression (p=0.2), atypical lymphocyte morphology (p=0.12). Although the follow-up is still short, ZAP-70 and IgVH status significantly predicted treatment-free interval (TFI), individually (p<0.01 and p<0.0001) and in combination (p<0.0001). Discordant cases showed a TFI similar to the better prognosis group, ZAP-70-/IgVH mutated (p<0.66). Thus, CLL with discordant features regarding ZAP-70 and IgVH status are mostly ZAP-70+/IgVH mutated, have a low incidence of poor risk genetic abnormalities del(17)p/del(11q) and a relatively long TFI, suggesting that the mutational status is more relevant than ZAP-70 in the clinical outcome of this category of patients.