Immunophenotyping of Cytologic Specimens by Flow Cytometry in Patients with or without Prior Hematologic Malignancy: A Retrospective Study

Introduction: Cytopathologists are frequently confronted with lymphocyte-rich effusions, and definite decision of reactive lymphocytosis or indolent lymphoma may be extremely difficult based on microscopy alone, where small proportions of malignant cells can be detected by flow cytometry. The study aimed to confirm the diagnosis of leukemia or lymphoma in body fluids and fine needle aspirate (FNA) specimens using multiparametric flow cytometry (MFC) immunophenotyping, which is a powerful tool for detecting hematologic malignancies.

Methods: Body fluids and FNA specimens simultaneously obtained for MFC, cytologic analysis and Real time PCR from 30 patients were submitted to flow cytometry laboratory from January 2017 to September 2019. The samples were 16 body fluids (11 pleural fluids; 5 ascetic fluids) and 14 FNA samples (13 lymph nodes; 1 lung mass). A panel of fluorochrome monoclonal antibodies against lymphoma and leukemia markers were used. The cases were diagnosed as leukemia or lymphoma according to the revised WHO classification of tumors of hematopoietic and lymphoid tissues (2016) guideline.

Results: Among 30 cases, 27(90%) showed immunophenotype consistent with malignancy. Mycobacterium tuberculosis DNA was positive in 3(10%) cases. Pleural fluid (n=11) samples were positive for 4 diffuse large B-cell lymphoma (DLBCL), 4 angioimmunoblastic T-cell lymphoma (AITL), 1 T-lymphoblastic lymphoma (T-LbLy), 1 thymoma, 1 tuberculosis. Ascetic fluid (n=5) samples showed positivity for 4 AITL and 1 DLBCL. FNA (n=14) were positive for 2 T-LbLy, 2 AITL, 3 DLBCL, 1 Classical Hodgkin lymphoma, 1 nodular lymphocyte predominant Hodgkin lymphoma, 1 peripheral T-cell lymphoma (NOS), 1 splenic B-cell marginal zone lymphoma, 1 neuroendocrine malignancy, 2 tuberculosis. Both immunophenotype and cytomorphology positive for malignancy were in 19/30(63.33%) cases. Cytomorphology was negative/ suspicious in 11/30(36.67%) cases, of which immunophenotype positive cases were 8/30(26.67%).

Conclusion: Multiparametric flow cytometry is invaluable tool to diagnose hematologic malignancies in SCEs/FNA as malignant cells can be missed out by cytomorphology.