[1348] CD45 Expression in Plasma Cell Myeloma: Comparison of Flow Cytometry and Immunohistochemistry and Relationship to Prognostic Factors.

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

Background: Reported rates of CD45 expression in plasma cell myeloma (PCM) are widely variable, ranging from 6-75% in published data, and the impact of CD45 expression on outcome is controversial. Flow cytometric analysis of CD45 in PCM is confounded by the often prominent autofluorescence of plasma cells (PCs) and PC adherence to normal CD45(+) populations, such as granulocytes and monocytes. Therefore, we rigorously examined CD45 expression by flow cytometry (FC) in PCMs, controlling for these artifacts, and additionally compared the FC findings with CD45 immunohistochemistry (IHC). CD45 expression was then compared to known PCM prognostic indicators.
Design: CD45 expression was evaluated in marrow aspirates of diagnostic/previously untreated PCMs with ≥20% PCs by differential count. PCs were evaluated by 4-color FC with antibodies against CD19, CD20, CD38, CD45, CD56, and cytoplasmic light chains. Antigen expression was defined as ≥20% positivity compared to an isotype control containing CD38. PC/granulocyte doublets were excluded from analysis if they had distinct CD45/light scatter properties compared to the PC cluster. CD45 IHC was classified as diffusely (+); partial (+) when containing clusters (>5) of CD45(+) PCs; or negative (<5%, non-clustered CD45(+) PCs). Cytogenetic, β2microglobulin, clinical stage, and immunophenotypic data were collected.
Results: 49 PCMs (42 diagnostic, 7 previously untreated) were evaluated (27 females and 22 males, 35-86 y/o, median 62 y/o). CD45 was (+) in 27/49 cases (55%) by FC and 8/49 (16%) by IHC. Of the 8 IHC(+) case, 5/8 were partial (+) and 3/8 were diffusely (+); all 8 were CD45(+) by FC. All cases with 17p deletion were CD45(+) by FC (6/6), versus 21/43 cases lacking 17p deletion (p=0.027). 24/27 FC CD45(+) cases were also CD56(+), compared to 13/22 CD45(-) cases (p=0.02) CD45 expression showed no association with age, β2-microglobulin, diploidy status, presence of t(11;14)/t(4;14)/monosomy13 by FISH, ISS or Durie-Salmon stage, or CD19 and CD20 expression. CD45 expression by IHC was not associated with any other variables.
Conclusions: CD45 expression by FC is observed in 55% of untreated/diagnostic PCMs, when rigorously controlling for artifacts, which is higher than most reports in the literature. FC is much more sensitive for CD45 expression than IHC. Interestingly, CD45 expression by FC was associated with 17p deletions by FISH, a well recognized poor prognostic factor. An association was additionally observed between CD45 and CD56 expression by FC.
Category: Hematopathology

Tuesday, March 1, 2011 9:30 AM

Poster Session III # 241, Tuesday Morning


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