[1299] Immunophenotypic Analysis of Systemic Mastocytosis by High-Sensitivity Flow Cytometry.

Svetlana Kondratiev, Betty Li, David M Dorfman, Olga Pozdnyakova. Brigham and Women's Hospital, Boston, MA

Background: Systemic mastocytosis (SM) represents a spectrum of myeloproliferative disorders that is characterized by multifocal dense aggregates of mast cells in the extracutaneous sites, a major criterion for the diagnosis. In the absence of the major criterion, the diagnosis of SM relies on the presence of at least three minor criteria that, among others, include aberrant expression of CD2 and CD25 on the neoplastic mast cells. Although flow cytometry (FC) has become a rapid and reliable modality for immunophenotyping of mast cells, very often the analysis is hindered by the low numbers of abnormal cells present in the specimen. We employed a high sensitivity flow cytometric approach for detection of CD2 and CD25 on mast cells in bone marrow (BM) aspirates and compared the data to the concurrent BM biopsies.
Design: Flow cytometric analysis was performed on 37 BM samples of suspected or known cases of SM. In each case, approximately 1,000,000 events were studied and expression of CD2 and CD25 was examined on CD117-bright cells. The analysis was interpreted as positive when a discrete population of CD25 and/or CD2-positive cells was seen compared to the isotype control. These results were compared to the BM biopsy and aspirate smear findings. In addition to morphologic findings, CD117 and mast cell tryptase stains were performed on the BM biopsies.
Results: Based on the BM biopsy findings, 16 cases were positive for SM with 8 of these cases (50%) detected by FC. Out of the remaining 8 cases that were interpreted as negative by FC, only three showed significant involvement by neoplastic mast cells (greater than 30%); the majority of these cases had minimal involvement as confirmed by mast cell tryptase and CD117 stains performed on the BM biopsies. All three cases that were interpreted as suspicious by FC remained suspicious on the concurrent BM biopsy.

Comparison of bone marrow involvement by systemic mastocytosis by flow cytometry and morphologic analyses.
 BM Flow CytometryBM BiopsyBM Aspirate
Positive8 (22%)16 (43%)9 (24%)
Suspicious3 (8%)3 (8%)7 (19%)
Negative26 (70%)18 (49%)21 (57%)

Conclusions: Detection of systemic mastocytosis by flow cytometric analysis is limited by percent bone marrow involvement by neoplastic mast cells with increased sensitivity in the cases with greater than 30% involvement. The overall sensitivity of FC was 50%, with CD25 being the most common aberrant marker detected. Flow cytometric immunophenotypic analysis is especially relevant when the use of Zenker's fixative or similar reagents precludes CD2 and CD25 immunohistochemical analysis BM biopsies.
Category: Hematopathology

Monday, February 28, 2011 1:00 PM

Poster Session II # 181, Monday Afternoon


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