ZAP-70 as a prognostic laboratory biomarker in chronic lymphocytic leukemia: flow-cytometric assessment, clinical utility, and standardization challenges.

Chronic lymphocytic leukemia (CLL) is a heterogeneous haematological malignancy characterized by variable rates of progression, treatment requirements and survival. Zeta-chain-associated protein kinase 70 (ZAP-70) is a biologically informative marker historically associated with aggressive CLL biology, although it is no longer considered a standard-of-care prognostic marker where contemporary molecular prognostic testing is available. This review examines the role of ZAP-70 in the laboratory assessment, prognosis and clinical management of CLL, focusing on flow-cytometric measurement and integrated risk stratification. We synthesize the available literature and data showing that increased B-cell receptor signaling and ZAP-70 expression are correlated with shorter time to first treatment, disease progression and inferior survival, as well as with unmutated immunoglobulin heavy-chain variable-region genes. We further evaluate its prognostic value in relation to CD38, CD49d, β2-microglobulin, TP53 disruption, fluorescence in situ hybridization abnormalities and Rai and Binet staging. Laboratory factors that affect clinical implementation are discussed, such as antibody clone selection, fixation and permeabilization, gating strategies, internal controls, positivity thresholds and quantitative reporting. We also examine complementary assessment by quantitative PCR, immunohistochemistry and DNA methylation analysis, as well as the evolving role of ZAP-70 in the targeted-therapy era. The implementation of ZAP-70 assessment in laboratory practice requires harmonized analytical workflows, standardized interpretation and prospective validation. This review provides a laboratory-medicine perspective on the historical and biological relevance of ZAP-70, its analytical limitations, and its restricted contemporary role, including possible adjunctive use where molecular prognostic testing is delayed or unavailable.