Diagnostic Challenges in Nodal T-Follicular Helper (TFH) Cell Lymphoma

Nodal T-follicular helper cell lymphomas comprise a biologically similar but morphologically diverse family of T-cell neoplasms, including angioimmunoblastic T-cell lymphoma, nodal T-follicular helper cell lymphoma, follicular-type, and nodal TFH lymphoma, not otherwise specified. Despite recurrent molecular alterations involving RHOA, IDH2, TET2, and DNMT3A, the diagnosis of TFH lymphomas remains challenging because of their mimicry of other lymphoid neoplasms and reactive lymphadenopathy. A key pitfall is confusion with classical Hodgkin lymphoma, as admixed Epstein–Barr virus-positive large B-cells with Reed–Sternberg cell-like morphology and immunophenotype can be found in TFH lymphomas. Similarly, follicular-type TFH lymphoma is often misclassified as follicular B-cell lymphoma unless T-cell lineage is investigated by immunophenotyping and the absence of BCL2 or BCL6 rearrangement is established. The ‘not otherwise specified’ category should be reserved for cases with proven T-follicular helper immunophenotype but lacks definitive angioimmunoblastic or follicular architecture. Comparing current frameworks, 5th edition of the World Health Organization classification permits rare CD4/CD8 double negative cases, while International Consensus Classification requires CD4 positivity. Some of these distinctions may appear taxonomic as all T-follicular helper T-cell lymphoma subtypes share molecular alterations, prognosis, and treatment approach. However, these classifications are meaningful from the perspective of a histopathologic diagnosis as a wrong diagnosis may lead to ineffective treatment approach. Accurate recognition of these lymphomas prevents misclassification, avoids inappropriate regimens, and ensures eligibility for proper clinical trials. A structured approach integrating morphology, multiparameter immunohistochemistry, flow cytometry, and molecular testing provides the best safeguard against diagnostic pitfalls and refines classification across subtypes.