Pitfalls in Flow Cytometry: Diagnostic Challenges for a Pathologist
Beenu Thakral, Karan Saluja, Mohamed Eldibany, Irene J Check. NorthShore University HealthSystem; University of Chicago Pritzker School of Medicine, Chicago, Evanston, IL
Background: Flow cytometry (FC) is important in the diagnosis of lymphoma or leukemia, but results can be misinterpreted. The aim of this study was to identify uncommon diagnostic pitfalls.
Design: FC analyses performed for clinical suspicion of lymphoma or leukemia at our center between July, 2010 and June, 2011 were reviewed as a part of quality assurance. Cases with significant discordance between FC and morphologic results not explained by sampling were analyzed.
Results: 1362 specimens [bone marrow, blood, fine needle aspirate, body fluids, or lymph node and other tissue biopsies] were reviewed. Three unusual cases were identified as shown in table.
|Case 1||Case 2||Case 3|
|History||74/M with history of myelodysplasia||60/F with 3 cm PET+ bone mass. No prior history of cancer.||59/M with 8 cm retroperitoneal mass. No prior history of cancer.|
|Specimen||BM||FNA of mass||FNA of mass|
|Clinical impression||MDS progression to leukemia||Plasmacytoma||Lymphoma|
|FC results||38% blasts, (CD45dim+, CD34+, CD13dim+, CD117-, CD33-, HLADR-), consistent with acute leukemia.||30% plasma cells (CD45-, CD38+, CD138+, CD3-, CD19-,CD20-, κ-, λ-).||Nondiagnostic. 90% large CD45- cells, unusually high side scatter. Dimly+ for CD20, CD38, CD138, dual (nonspecific) staining for κ, λ.|
|Pathology results||BM biopsy showed only 10% CD34+ blasts. MDS with numerous CD34+ CD61+ dysplastic megakaryocytes.||Metastatic adenocarcinoma. Cells had plasmacytoid morphology, but MUM1-, κ-, λ- and CD138dim+. Cytokeratin stains (AE1/AE3, CK7) and TTF1 were positive.||Large B-cell lymphoma with Burkitt-like features. Large, atypical lymphoid cells, high N/C ratio, nuclei with irregular outlines, discernible nucleoli, and vacuoles in cytoplasm.|
|Resolution of discrepancy||Erroneously high CD34+ blast count on FC was due to fragments of dysplastic CD34+ megakaryocytes with light scatter properties of lymphocytes/blasts.||Carcinoma cells expressed CD138 and were misinterpreted as plasma cells on FC.||PET scan showed a 5 cm testicular mass prompting re-biopsy of the retroperitoneal mass. On IHC, large cells were CD117+, Oct3/4+, PLAP+, consistent with metastatic seminoma.|