Pan B-Cell Markers Are Not Redundant in Analysis of Chronic Lymphocytic Leukemia (CLL)

Background: The classic immunophenotype for chronic lymphocytic leukemia (CLL) is CD19⁺, restricted dim surface expression of kappa or lambda light chain, CD5⁺, CD23⁺, dim CD20⁺, negative FMC7, and negative CD79b. However, the necessity of assaying for all 3 pan B-cell markers (CD20, FMC7, and CD79b) by flow cytometry has not been definitively documented for CLL. Methods: Qualitative patterns and semi-quantitative assessment of staining intensity for CD20, FMC7 and CD79b were performed in 70 cases with a current or prior diagnosis of CLL or CLL with increased prolymphocytes leukemia (CLL/PL). The concurrent morphology in 66 of 70 specimens was classified as typical CLL in 53 cases, CLL/PL in 10 cases, and large cell lymphoma in 3 cases. Results: Forty percent of the cases varied from the characteristic immunophenotype by having moderate or bright staining of CD20 (36%), FMC7 (7%), and/or CD79b (18%). Discrepant qualitative staining patterns were found between FMC7 and CD20 (21%), CD20 and CD79b (15%), and CD79b and FMC7 (10%). Semiquantitative measurement of staining intensity showed little correlation between CD79b and CD20 or FMC7. Moderate correlation was seen between CD20 and FMC7. No correlation was observed between morphology and intensity of marker expression. Conclusions: Variable patterns and intensity of staining were seen for FMC7, CD20, and CD79b in this cohort of CLL samples. Dim or negative staining was most consistently seen for FMC7 (93% of specimens). Although FMC7 staining intensity was moderately correlated with CD20, CD79b intensity was poorly correlated with either CD20 or FMC7, and thus, may provide some independent information.