en Pathology Pathology پژوهشي Original Article Background: Immunophenotyping in the rare group of nodal Peripheral T-cell Lymphomas (PTCL) exposes interesting features such as T-cell marker downregulation and paradoxically, the presence of reactive, clustered large-sized CD20 positive B-cells (B-cell proliferation). Epstein-Barr virus (EBV) has been suggested as a putative etiology in pathogenesis of B-cell lymphoma. We aimed to review the immunohistochemical profile of patients with nodal PTCL with emphasis on T-cell markers and immunophenotypic aberrations, CD20 positive large B-cells, Ki-67 scores (as a measure of proliferation index) and to assess the association of Epstein-Barr virus in various subtypes of nodal PTCL.<br> Methods: 80 cases of nodal PTCL diagnosed during January 2008-June 2013 were included in the study. Relevant clinical and hematological data were collected. Using Streptavidin-Biotin-Peroxidase system, staining for CD2, CD3, CD4, CD5, CD7, CD8, CD20,EBV-LMP1 and Ki-67 were performed on all blocks.CD10,CD23,Bcl-6, CD30 and ALK-1 were used in relevant cases.<br> Results: 95% of patients had downregulation of at least one T-cell marker (maximum: CD7 (87%), minimum: CD3 and CD5- 9% each). 29 patients (36%) showed markers of B-cell proliferation. Only five patients (6%) were positive for EBV-LMP1. There was a significant association between EBV-LMP1 positivity and B-cell proliferation (P=0.002). 17 patients (21%) had high Ki-67 index (&ge;80%).<br> Conclusion: Nodal PTCL showed frequent downregulation of T-cell markers. EBV was only infrequently positive in these Lymphomas. Clusters of large B-cells need to be noted in pathology reports and EBV needs to be tested for in such cases. Peripheral T-cell lymphoma, Immunophenotyping, Epstein-Barr virus, Angioimmunoblastic T-cell lymphoma, Anaplastic large cell lymphoma, Anaplastic lymphoma kinase 101 108 http://ijbc.ir/browse.php?a_code=A-10-445-1&slc_lang=en&sid=1 Bidish Kumar Patel nappingbee@gmail.com 10031947532846004957 10031947532846004957 No Post Doctoral Fellow in Department of Cytogenetics Debdatta Basu ddbasu@gmail.com 10031947532846004958 10031947532846004958 No Senior Professor of Pathology Rakhee Kar drrakheekar@gmail.com 10031947532846004959 10031947532846004959 No Additional Professor of Pathology Biswajit Dubashi drbiswajitdm@gmail.com 10031947532846004960 10031947532846004960 Yes Additional Professor of Medical Oncology