ZAP-70 (zeta-associated protein-70) is a surrogate marker for the somatic mutation status of immunoglobulin heavy chain (IGHV) in CLL.  Unfortunately, attempts to utilize flow cytometry for this purpose has resulted in unreliable results.  ZAP-70 expression by IHC has been shown to have an increased risk of progression to therapy requirement (3-yr risk 83% vs. 31% for ZAP-70 negative) [Modern Pathology (2010)23,1518-1523].  ZAP-70 expression is not specific to CLL, and is not particularly useful for tumor sub-classification/prognosis outside the setting of CLL.

 

ZAP-70 expression in B-cell lymphoid neoplasms (Carreras, J, et al).

ZAP-70 is interpreted as negative or positive.  The minimum positive expression is weakly positive( 1+) staining defined as granular cytoplasmic staining with nuclear blush in a majority of tumor cells.  Strong positivity (2+) is  defined as strong expression in a majority of tumor cells.

 

ZAP-70 will also stain T-cells in the background.  Therefore, ZAP-70 should be interpreted with the accompaniment of CD3 and CD20, so that there is clear discernment between tumor and background lymphoid cells.

 

One of the big problems to identify ZAP-70 expression in CLL is the material available for evaluation.  Most material is based on peripheral blood, and flow cytometry has been difficult to analyze reliably for ZAP-70 expression.  An alternative is to perform PERIPHERAL BLOOD MONONUCLEAR CELL (PBMC) PURIFICATION AND CELL BLOCK PREPARATION as described by Roullet, et. al. in which a cell block is prepared from peripheral blood on which IHC for ZAP-70 can be reliably performed.  Please review Roullet’s article for complete technical details.

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Admirand, J. H., Knoblock, R. J., Coombes, K. R., Tam, C., Schlette, E. J., Wierda, W. G., et al. (2010). Immunohistochemical detection of ZAP70 in chronic lymphocytic leukemia predicts immunoglobulin heavy chain gene mutation status and time to progression. Modern Pathology : an Official Journal of the United States and Canadian Academy of Pathology, Inc, 23(11), 1518–1523. doi:10.1038/modpathol.2010.131 

 

Carreras, J., Villamor, N., Colomo, L., Moreno, C., Ramón y Cajal, S., Crespo, M., et al. (2005). Immunohistochemical analysis of ZAP-70 expression in B-cell lymphoid neoplasms. The Journal of Pathology, 205(4), 507–513. doi:10.1002/path.1727

 

Roullet, M., Sargent, R., Pasha, T., Cajiao, I., Elstrom, R., Smith, T., et al. (2007). ZAP70 expression assessed by immunohistochemistry on peripheral blood: a simple prognostic assay for patients with chronic lymphocytic leukemia. Applied Immunohistochemistry & Molecular Morphology : AIMM / Official Publication of the Society for Applied Immunohistochemistry, 15(4), 471–476. doi:10.1097/01.pai.0000213152.41440.34 

 

Crespo, M., Bosch, F., Villamor, N., Bellosillo, B., Colomer, D., Rozman, M., et al. (2003). ZAP-70 expression as a surrogate for immunoglobulin-variable-region mutations in chronic lymphocytic leukemia. The New England Journal of Medicine, 348(18), 1764–1775. doi:10.1056/NEJMoa023143