[1443] Immunophenotypic Stability in Plasma Cell Myeloma by Flow Cytometry

MD Spears, H Olteanu, SH Kroft, AM Harrington. Medical College of Wisconsin, Milwaukee, WI

Background: The utility of flow cytometry (FC) in the diagnosis and detection of residual disease in plasma cell myeloma (PCM) is well established; however, little data exists on the temporal stability of antigens commonly assessed in follow-up analyses. This study aims to evaluate follow-up PCMs for immunophenotype (IP) shifts utilizing a broad panel of antibodies.
Design: Using 4-color (6 parameter) FC, we retrospectively analyzed diagnostic and (+) follow-up PCMs. (+) follow-ups were defined by light chain restriction, 0.5 < κ/λ > 4.0. Plasma cells (PCs) were defined as CD38(bright+) events. IP stability was assessed in the following antigens: CD19, CD20, CD38, CD45, CD56, and cytoplasmic kappa and lambda light chains. A change in IP was defined as a gain, loss, or change in level of expression (at least half log shift) of an antigen between analyses. Isotype control tubes containing CD38 were used in all analyses. Whenever possible, background polytypic PCs were accounted for.
Results: 117 (+) FC analyses were reviewed from 48 PCM patients (pts) (31 males, 17 females) with a median age of 60 years (33-71), median time from diagnosis/first institutional encounter to follow-up of 6.6 mos (1.1-31.8), and median time between analyses of 4.9 mos (0.9-28). Follow-up studies ranged from 2-5/pt (median 2). By FC, PCs averaged 5.0% (0.01-83%, median 0.57%) of events. An IP change was observed in 16/48 (33%) pts, with single IP changes in 13/16 (81.3%), 2 changes in 1 pt (1/16, 6.3%), and 3 changes in 2 pts (2/16, 12.5%). Changes in CD45 occurred in 12/48 (25%) pts, including 5 changes in level of expression, 4 gains, 1 loss, and 2 pts with 2 changes over time (both gains followed by losses). Gains of CD19 occurred in 3/48 (6.3%) pts. CD56 changes were seen in 3/48 (6.3%) pts, including 1 loss, 1 gain, and 1 change in level of expression. CD20 changes were present in 3/48 (6.3%) pts, with 2 gains and 1 loss. 1 pt demonstrated a switch in light chain expression (lambda to kappa), from an analysis 3 mos prior, with corresponding switches in M protein and serum free light chains, despite morphologic stability of disease. The median time from diagnostic analysis to IP change was 6.7 mos (1.7-17.2).
Conclusions: A third of PCM cases with (+) follow-up FC studies show IP change over time. CD45 is the least stable antigen. Importantly, changes in aberrant antigen expression, such as loss or gain of CD56 and gain of CD20, can be seen. Our data illustrates the potential evolution of the IP in PCM and the importance of recognizing such when evaluating for residual disease.
Category: Hematopathology

Tuesday, March 23, 2010 9:30 AM

Poster Session III # 209, Tuesday Morning


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