An Approach to Nodal T- and NK-Cell Lymphomas—A Systemic Review

Abstract T-cell lymphomas are rare neoplasms that have complex pathology. The multiparameter approach has been recommended by World Health Organization (WHO) for the classification of T-cell lymphomas taking into account morphology, immunophenotype, genetics, and clinical features. This also includes division established on the possible cell-of-origin (COO) from T regulatory or T-follicular helper (TFH) cells. The recent WHO-HAEM5 has classified entities as precursor T-lymphoblastic neoplasms, mature T-cell neoplasms, Epstein-Barr virus (EBV)-related T- and NK/T-cell lymphomas, and tumor-like lesions with T-cells predominance. Distinct entities have been recognized within the anaplastic large cell lymphoma (ALCL) family founded on the status of anaplastic lymphoma kinase (ALK) gene rearrangement: ALK-positive and molecularly heterogeneous ALK-negative. The family of lymphomas arising from TFH cells consists of three distinct nodal TFH cell lymphoma entities: angioimmunoblastic-type, follicular-type, and not otherwise specified. These three entities show significant clinical and immunophenotypic overlap. The cases that do not qualify for ALCL or nodal TFH cell lymphomas are labelled as peripheral T-cell lymphomas-not otherwise specified after ruling out nodal EBV-positive T- and NK- cell lymphoma. The new category termed tumor-like lesions with T cell predominance has a high chance to be misdiagnosed as lymphoma. This category includes entities such as Kikuchi-Fujimoto disease, indolent T-lymphoblastic proliferation, and autoimmune lymphoproliferative syndrome. For pathologists, diagnosing nodal T-cell lymphomas may be thought-provoking due to their broad histopathologic spectrum that mimics reactive as well as other neoplastic processes. This review provides a comprehensive diagnostic criterion of the most commonly encountered nodal T-cell and NK cell lymphomas in day-to-day training and an algorithmic approach.