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Using the geometric mean fluorescence intensity index method to measure ZAP-70 expression in patients with chronic lymphocytic leukemia

Authors Wu Y, Wang H, Liang J, Miao Y, Liu L, Qiu H, Chun Q, Wang R, Li J

Received 17 August 2015

Accepted for publication 10 November 2015

Published 18 February 2016 Volume 2016:9 Pages 797—805


Checked for plagiarism Yes

Review by Single-blind

Peer reviewers approved by Dr Ram Prasad

Peer reviewer comments 2

Editor who approved publication: Dr William Cho

Yu-Jie Wu, Hui Wang, Jian-Hua Liang, Yi Miao, Lu Liu, Hai-Rong Qiu, Chun Qiao, Rong Wang, Jian-Yong Li

Department of Hematology, First Affiliated Hospital of Nanjing Medical University, Jiangsu Province Hospital, Nanjing, People’s Republic of China

Abstract: Expression of ζ-chain-associated protein kinase 70 kDa (ZAP-70) in chronic lymphocytic leukemia (CLL) is associated with more aggressive disease and can help differentiate CLL from cases expressing mutated or unmutated immunoglobulin heavy chain variable region (IgHV) genes. However, standardizing ZAP-70 expression by flow cytometric analysis has proved unsatisfactory. The key point is that ZAP-70 is weakly expressed with a continuous expression pattern rather than a clear discrimination between positive and negative CLL cells, which means that the resulting judgment is subjective. Thus, in this study, we aimed at assessing the reliability and repeatability of ZAP-70 expression using the geometric mean fluorescence intensity (geo MFI) index method based on flow cytometry with 256-channel resolution in a series of 402 CLL patients and to compare ZAP-70 with other biological and clinical prognosticators. According to IgHV mutational status, we were able to confirm that the optimal cut-off point for the geo MFI index was 3.5 in the test set. In multivariate analyses that included the major clinical and biological prognostic markers for CLL, the prognostic impact of ZAP-70 expression appeared to have stronger discriminatory power when the geo MFI index method was applied. In addition, we found that ZAP-70-positive patients according to the geo MFI index method had shorter time to first treatment or overall survival (P=0.0002, P=0.0491). This is the first report showing that ZAP-70 expression can be evaluated by a new approach, the geo MFI index, which could be a useful prognostic method as it is more reliable, less subjective, and therefore better associated with improvement of CLL prognostication and prediction of clinical course.

Keywords: chronic lymphocytic leukemia, ZAP-70, flow cytometry, prognosis, geometric mean fluorescence intensity index

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