CLL/SLL represents a B-cell neoplasm of small lymphocytes which involve a combination of peripheral blood, bone marrow, and/or lymph nodes. When peripheral blood predominates, then it is referred to as CLL, and when it presents as predominately nodal involvement it is referred to as SLL. This is the same disorder with different manifestations.
Monoclonal B-cell lymphocytosis (MBL) was defined by the International Familial CLL consortium in 2005 as a monoclonal B-cell lymphocyte population in the peripheral blood <5,000/uL without evidence of lymphadenopathy (i.e. SLL), an autoimmune/infectious disease or other features diagnostic of a B-cell lymphoproliferative disorder. The 2016 WHO hematopathology revision dropped the requirement of cytopenias or disease related symptoms as adequate to make the diagnosis of CLL.
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).
Lymphoid Disorder
No.
ZAP-70 + (%)
Lymphoblastic Lymphoma
7
28%
Chronic Lymphocytic Leukemia
52
65%
Mantle Cell Lymphoma
36
8%
Classical
28
11%
Blastoid
8
0%
Follicular Lymphoma
19
0%
Marginal Zone Lymphoma
23
4%
MALT
11
0%
Nodal
5
20%
Splenic
7
0%
Diffuse Large B-Cell Lymphoma
45
2%
Burkitt Lymphoma
29
31%
Hodgkin Lymphoma
14
0%
Stain Interpretation
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.
IHC on Peripheral Blood
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.
Photomicrographs
ZAP-70 – Benign TonsilZAP-70 weak expression in CLL with an unmutated IgVH gene (poor prognosis). Strong staining in background T-cells.ZAP-70 weak expression in CLL with an unmutated IgVH gene (poor prognosis)
References
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
