[1309] CD23 Expression in Plasma Cell Myeloma Is Specific for Abnormalities of Chromosome 11, and Is Associated with Primary Plasma Cell Leukemia in This Cytogenetic Sub-Group

MP Walters, H Olteanu, P Van Tuinen, SH Kroft. Medical College of Wisconsin, Milwaukee, WI

Background: CD23, a low-affinity Fc receptor for IgE, plays a pivotal role in IgE homeostasis. It is present on a subset of B-cells, as well as on some activated T cells, monocytes, Langerhans cells, eosinophils, and macrophages. CD23 expression has been well-characterized in non-Hodgkin lymphoma, and has diagnostic utility in the distinction of chronic lymphocytic leukemia and mantle cell lymphoma. However, to our knowledge, CD23 expression has not been previously studied in plasma cell myeloma (PCM).
Design: Fifty diagnostic bone marrows containing PCM (including 4 cases of primary plasma cell leukemia (PCL)) were evaluated for CD23 expression by immunohistochemistry (IHC). CD23 was also evaluated by flow cytometry (FC) in select cases. Additional immunophenotypic features were derived from routine FC performed at diagnosis, and included assessment of CD19, CD20, CD45, and CD56 in most cases. Expression of CD23 was correlated with presenting laboratory data and cytogenetic findings.
Results: Five PCM cases (10%) expressed CD23 by IHC; FC analysis performed in two of these confirmed the CD23 expression. In all 5 cases, CD23 expression was strong and uniform on the PCM cells. Compared to negative cases, CD23(+) PCM was more likely to express CD19 (2/5 vs 0/41; p=.01) and less likely to express CD56 (1/5 vs 33/43; p=.021). Three of 4 cases of primary PCL expressed CD23 (p=.002). Four of the 5 CD23 (+) harbored a t(11;14), and the fifth had a +11. Six CD23 negative cases also contained a t(11;14). Among t(11;14) (+) cases, there were no significant differences in immunophenotype and presenting laboratory data (blood counts, M-protein level, creatinine, beta-2 microglobulin, calcium) between CD23(+) and CD23(-) cases. Overall, t(11;14) (+) PCM was more likely to express CD20 (4/10 vs 2/35, p=.016) and less likely to express CD56 (4/10 vs 29/36, p=.02). Compared to non-leukemic PCM, PCL was associated with expression of CD45 (4/4 vs 16/39, p=.039) and CD19(2/4 vs 0/42, p=.006), and less frequent CD56 (1/4 vs 33/44, p=.069).
Conclusions: CD23 is expressed by neoplastic plasma cells of PCM in 10% of cases, and shows a strong association with abnormalities of chromosome 11, particularly the t(11;14), and with primary PCL. Our study corroborates previously reported associations of t(11;14) with expression of CD20 and lack of CD56 in PCM. The biologic role of CD23 in PCM remains to be determined. CD23 could represent a therapeutic target in the subset of positive cases.
Category: Hematopathology

Wednesday, March 11, 2009 9:30 AM

Poster Session V # 206, Wednesday Morning