From Slides to Scatter Plots: Correlating Immunohistochemistry and Flow Cytometry Findings in Tissue Biopsies: A Study of 47 Cases.

INTRODUCTION: Histopathology with immunohistochemistry (IHC) remains the gold standard for diagnosing hematologic malignancies on tissue biopsy, but interpretation can be subjective and time-consuming. Flow cytometry (FCM) offers rapid, multiparametric, single-cell analysis and may complement IHC. AIMS AND OBJECTIVE: To evaluate the diagnostic concordance and performance of FCM compared with IHC in tissue biopsies from patients with suspected haematological malignancies, and to assess the utility of integrating both modalities for improved diagnostic accuracy. METHODS: A prospective observational study was conducted on 47 biopsy specimens (lymph node and extranodal) from patients clinically suspected of haematological malignancy between July 2021 and April 2025. Each sample underwent parallel evaluation by FCM and histopathology with IHC. Diagnostic concordance, sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were calculated using IHC as the gold standard. RESULTS: Overall concordance between FCM and IHC was 57.4%, with a sensitivity of 48.57%, specificity of 83.33%, PPV of 89.4%, and NPV of 35.71%. For non-Hodgkin haematological neoplasms, concordance improved to 73.91% and sensitivity to 80.95%. Complete agreement was observed in all B-ALL and myeloid sarcoma cases, while discordance was common in Hodgkin lymphoma and non-haematological malignancies. CONCLUSION: Flow cytometry provides rapid, objective, and highly specific diagnostic information in suspected lymphoid malignancies, particularly non-Hodgkin neoplasms. While it cannot replace IHC in Hodgkin lymphoma and non-haematological tumours, integrating both modalities enhances diagnostic accuracy and supports timely clinical management.