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[2116] 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.
BM = Bone marrow, FC = Flow cytometry, FNA = Fine needle aspirate

Conclusions: These cases revealed dysplastic CD34+ megakaryocyte fragments that mimic blasts, metastatic CD138+ adenocarcinoma cells that look like plasma cells, and a metastatic germ cell tumor imitating large B lymphoma. They underscore the value of resolving any discrepancies among FC, clinical, and morphologic findings when rendering a diagnosis.
Category: Quality Assurance

Monday, March 19, 2012 1:00 PM

Poster Session II # 265, Monday Afternoon

	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.

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