[1330] CD200 Expression in Plasma Cell Myeloma.

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

Background: CD200 is a membrane protein with immunosuppressive function. Based on a single microarray study, the majority of plasma cell myelomas (PCMs) are CD200(+), and patients (pts) that lack CD200 show a longer event-free survival (EFS). Because there is a paucity of literature data and CD200 is a potentially useful prognostic and minimal residual disease marker, we studied the expression of CD200 by flow cytometry (FC) and immunohistochemistry (ICH) and correlated it with clinicopathologic parameters.
Design: 72 consecutive PCM bone marrow (BM) biopsies (42 new, 30 treated pts) were evaluated by 4-color FC with antibodies against CD19, CD20, CD38, CD45, CD56, CD117, CD200, and cytoplasmic light chains. Expression of CD200 was assessed in plasma cells (PCs) based on an isotype control tube containing CD38. 14 BM biopsies with polytypic plasmacytosis (PP) were used as reactive controls. IHC was performed with anti-human CD200 (R&D Systems, Minneapolis, MN).
Results: 44/72 (61%) PCMs were CD200(+). 14/72 pts had multiple FC analyses, and all showed conserved CD200 expression. All PCs in PP cases were CD200(-). By IHC, CD200(+) cases showed strong membrane positivity in the neoplastic PCs. FC and IHC showed concordant results in all but one case, which was dim CD200(+) by FC and CD200(-) by IHC. Results are summarized in Table 1.

Table 1.

Parameter	CD200(+)	CD200(-)
n (%)	44 (61.1%)	28 (38.9%)
*Age≥65 years	61.4%	32.1%
M:F	1.9	2.1
Kappa	68.2%	78.6%
IgA	22.7%	25.0%
B2M≤3.5 mg/L	59.5%	37.0%
B2M>5.5 mg/L	15.8%	37.0%
Albumin<35 g/L	31.6%	50.0%
*Hgb<10 g/dL	20.5%	53.4%
Bone lesions	76.9%	76.9%
C-reactive protein≥5 mg/L	25.0%	42.3%
BM PCs, median	50%	50%
CD19(-)	100%	96%
CD56(+)	79.5%	67.9%
CD20(+)	15.9%	14.3%
CD45(+)	52.4%	57.1%
CD117(+)	41.7%	23.0%

B2M - beta-2 microglobulin; * - p<0.05

A higher proportion of pts with CD200(+) PCMs were ≥65 years, and they presented with lower hemoglobin (Hgb), compared to those with CD200(-) PCM. The median EFS in pts treated with autologous stem cell transplant was shorter in CD200(+) than in CD200(-) PCMs: 15 vs. 27.5 months (p=0.038).
Conclusions: 61% of PCMs in our series are CD200(+) by FC, which is comparable to a previous study that included only limited FC data (15 pts). We confirm the CD200(-) immunophenotype of normal PCs, and demonstrate stability of CD200 expression in PCM pts with serial FC evaluations. The longer EFS in CD200(-) cases supports the findings from a previous study; the correlations of CD200 expression with age≥65 years and low Hgb constitute novel data. Finally, we validate CD200 IHC in a large series of PCMs.
Category: Hematopathology

Tuesday, March 1, 2011 8:30 AM

Platform Session: Section B, Tuesday Morning