[1248] Assessment of Bone Marrow Plasma Cells by Flow Cytometry, Fluorescence In Situ Hybridization, and Bone Marrow Morphology in 224 Cases for Diagnosis of Plasma Cell Neoplasms

G Lu, WR Stull, W Chen, XX Zhang. UT MD Anderson Cancer Center, Houston, TX; Medical Laboratory Services, Murrieta, CA; USLabs, Irvine, CA

Background: Bone marrow (BM) plasmacytosis is an important criterion for the diagnosis of plasma cell neoplasms (PCN). Although assessment of plasma cell (PC) percentages by BM morphologic examination (BMME) and flow cytometry (FC) are both important diagnostic tools, the results are often discrepant. Fluorescence in situ hybridization (FISH) assay using a multiple color panel is a sensitive method to detect genomic abnormalities in malignant plasma cells, and has important prognostic value. The aims of this study: (1) to assess the concordance of plasma cell percentages in bone marrow aspirates analyzed by BMME and by FC in cases of PCN; and (2) to determine if there is an optimal cut-off value for percentage of plasma cells assessed by FC in order to select cases for further analysis by FISH.
Design: Two hundred and twenty-four bone marrow aspirates with myeloma as indication were included in this study, and demonstrated monoclonal plasma cell population by 4-color flow cytometry analysis. They were also evaluated by FISH with a probe panel to detect +3, +5, +7, +11, del(13)(q14), del(17)(p13), and IgH locus rearrangements. Of the 224 cases, 157 were further studied by BMME. Plasmacytosis was defined as >3% PC on morphologic examination of Wright-Giemsa-stained aspirate smears, with 3-9% PC defined as mild, 10-30% as intermediate, and >30% as severe.
Results: Of the 157 cases, 40 showed mild plasmacytosis, 49 intermediate, and 68 severe; whereas 99 (63.1%) were FISH-positive including 6 cases with mild plasmacytosis (15%), 29 intermediate (59.2%), and 64 severe (94.1%). Plasma cells less than 2% by FC were found in 52 cases that were also evaluated by BMME. Thirty-three of the 52 showed morphologic plasmacytosis, including 21 that were mild, 11 intermediate, and 1 severe. Eight of the 33 cases were FISH-positive, accounting for 8.1% of the total FISH-detectable cases. Three of the 8 cases demonstrated adverse genomic abnormalities including del(13q) and non-t(11;14) IgH rearrangements.
Conclusions: Our results suggest that flow cytometry significantly underestimates plasma cell percentages in bone marrow. Using a PC cutoff of as low as 2% assessed by flow cytometry as an indication for further FISH analysis, at least 8% of FISH-detectable cases would have be missed.
Category: Hematopathology

Wednesday, March 11, 2009 9:30 AM

Poster Session V # 199, Wednesday Morning