Quantification of ZAP-70 mRNA by real-time PCR is a prognostic factor in chronic lymphocytic leukemia

Abstract

Background: Chronic lymphocytic leukemia (CLL) is heterogeneous with respect to prognosis and clinical outcome. Mutational status of immunoglobulin heavy chain variable region (IGHV) appears to be a particularly strong prognostic marker, but it is difficult to perform in a routine clinical laboratory. ζ-chain-associated protein kinase 70 kDa (ZAP-70) protein detected by flow cytometry is a strong surrogate marker of IGHV mutational status; however, it suffers from the lack of standardization.

Methods: We investigated whether ZAP-70 mRNA expression level can be a prognostic factor in CLL. Real-time quantitative polymerase chain reaction was used to analyze ZAP-70 mRNA expression from 102 CLL patients.

Results: The expression of ZAP-70 mRNA was significantly associated with Binet stage (P < 0.001), lactate dehydrogenase (P = 0.003), ZAP-70 protein (P = 0.018), IGHV mutational status (P = 0.038), and cytogenetic abnormality of del(17p13) or del(11q22.3) (P = 0.037) in CLL patients. According to receiver operating characteristic curve analysis for ZAP-70 mRNA and ZAP-70 protein, positive ZAP-70 mRNA (P = 0.006) was an adverse factor in determining the treatment free survival (TFS). In a multivariate Cox analysis of TFS, ZAP-70 mRNA is not ideal as an independent prognostic factor. However, ZAP-70 mRNA was statistically significant in predicting treatment response.

Conclusion: This study demonstrated the value of determination of ZAP-70 mRNA in providing useful prognostic information in CLL patients. However, ZAP-70 mRNA is not an independent prognostic factor.

Fig. 1

ROC curve analysis for ZAP-70 mRNA expression level and ZAP-70 protein measured by flow cytometry (AUC = 0.683, P = 0.018); chosen cut-off is indicated by the black arrow

Fig. 2

Treatment free survival (months) curve of patients with ZAP-70 mRNA-negative and ZAP-70 mRNA-positive