Pathological Diagnosis of Nodal T Follicular Helper Cell Lymphoma, Angioimmunoblastic Type.

We herein review the pathological diagnosis of nodal T follicular helper (TFH) cell lymphoma, angioimmunoblastic type (nTFHL-AI), a mature T-cell neoplasm with a TFH phenotype that was previously designated as angioimmunoblastic T-cell lymphoma (AITL). The history of AITL from its discovery to the WHO 5th classification, which includes Japanese pathologists' and hematologists' contributions, is discussed. We then focus on what true neoplastic T cells of nTFHL-Al are in histopathology. Since the number of neoplastic cells is small in some cases of nTFHL-AI, the findings of recent single-cell analyses to immunohistochemistry of TFH markers are considered. We also discuss Epstein-Barr virus large B-cells in AITL, particularly diffuse large B-cell lymphoma and classic Hodgkin lymphoma (CHL), and propose how to make a differential diagnosis between nTFHL-Al and CHL.