[1282] Flow Cytometric Analysis of Light Chain Expression Patterns in B-Cell Lymphomas Using Monoclonal and Polyclonal Antibodies.

Pedro Horna, Horatiu Olteanu, Steven H Kroft, Alexandra M Harrington. Medical College of Wisconsin, Milwaukee

Background: Analysis of light chain (LC) expression by flow cytometry (FC) is an essential tool in the diagnosis of B-cell non-Hodgkin lymphoma (B-NHL), with both monoclonal (mAbs) and polyclonal antibodies (pAbs) available for this purpose. While routinely using both mAbs and pAbs, we have observed NHLs that show LC restriction with one set, but lack LC expression with the other. The frequency and significance of this finding has not been systematically studied.
Design: We retrospectively analyzed body fluids, tissue, bone marrow (BM), lymph node (LN), and peripheral blood (PB) from B-NHLs, using two 4-color FC tubes: kappa mAb/lambda mAb/CD5/CD19 and lambda pAb/kappa pAb/CD20/CD38. Positivity for LC was determined by comparison to internal T cells. LC expression on non-neoplastic B cells served as an internal control.
Results: We analyzed 571 specimens from 441 patients: 236 chronic lymphocytic leukemia/small lymphocytic lymphomas (CLL/SLLs), 94 diffuse large B-cell lymphomas (DLBCLs), 61 follicular lymphomas (FLs), 29 mantle cell lymphomas (MCLs), 29 marginal zone lymphomas (MZLs), 20 lymphoplasmacytic lymphomas (LPLs), 12 splenic marginal zone lymphomas (SMZLs), 9 Burkitt lymphomas (BL), 6 hairy cell leukemias (HCL), and 75 other B-NHLs. Discrepancies in LC expression across tubes were seen in 41/571 cases (7.2%), including 22 (9.3%) CLL/SLLs, 1 (8.3%) SMZL, 8 (8.5%) DLBCLs, 4 (6.6%) FLs, 5 (6.7%) other B-NHLs, and 1 (3.5%) MZL, and were not present in BL, HCL, LPL, and MCL. 21/571 (3.7%) showed LC expression with only pAbs and 20/571 (3.5%) with only mAbs. Of 21 (-)mAb/(+)pAb cases, 15 (71%) were CLL/SLLs (p=0.006). Body fluids (5/29; 17%) were more likely to have LC discrepancies compared to tissues (8/100; 8%; p=0.17), BMs (13/170; 7.6%; p=0.15), PBs (12/154; 6.4%; p=0.07), and LNs (5/118; 4.2%; p=0.03). 42/571 B-NHLs (7.3%) were (-)mAb/(-)pAb, including 19/94 (20%) DLBCLs, 12/236 (5.1%) CLL/SLLs, and 2/61 (3.3%) FLs. 8/29 (28%) of body fluids were (-)mAb/(-)pAb, compared to 34/542 (6.3%) of other specimens (p=0.05).
Conclusions: Approximately 7% of B-NHLs analyzed by FC show discrepant LC expression when using both mAbs and pAbs, most commonly observed in fluids. Equal proportions of cases were LC (+) with only pAbs or mAbs. The (-)mAb/(+)pAb pattern was most frequent in CLL/SLLs, suggesting that dim LC expression is best detected with pAbs. Analyses that rely solely on one LC reagent are therefore limited, and may be responsible for the high rates of LC negativity described in the literature for DLBCL (up to 50%), compared to 20% in our series.
Category: Hematopathology

Tuesday, March 1, 2011 1:00 PM

Poster Session IV # 170, Tuesday Afternoon

 

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