Peripheral T-Cell Lymphomas with Follicular Growth Patterns Are Derived from Follicular Helper T Cells (TFH): A Link with Angioimmunoblastic T-Cell Lymphomas?.
Authors: Huang Yenlin , Moreau Anne , Dupuis Jehan , Streubel Berthold , Petit Barbara , Legouill S. , Martin-Garcia Nadine , Copie-Bergman Christiane , Gaillard Fanny , Baglin Anne-Catherine , Briere Josette , Roncador Giovanna , Haioun Corinne , Delfau-Larue Marie-Helene , Chott Andreas , Gaulard Philippe 
Published: October 2019

Abstract
Nodal peripheral T-cell lymphomas represent a heterogeneous category, composed of three entities: anaplastic large cell lymphomas, peripheral T-cell lymphomas unspecified (PTCLu) and angioimmunoblastic T-cell lymphomas (AITL). The later entity has been recently recognized to derive from follicular helper T cells (TFH). Among PTCLu - which represents an ill-defined entity - a peculiar form with follicular growth pattern (PTCL-F) has been recently reported, and one article stated their association with t(5 ;9)(q33 ;q22) involving ITK and SYK (Leukemia2006; 20: 313–318). However, the origin of tumor cells and clinical aspects of this group of PTCL-F are still unknown. The aim of this study was to analyse a series of PTCL-F to describe their clinical and histopathological aspects, to identify their cell of origin, and their relationship with AITL. Fourty-two patients from 32 to 85 years of age with 51 biopsies were selected from three Departments of Pathology (Creteil, n=24, Nantes n=13, Vienna n=14). All patients showed histopathologic features of PTCL-F in at least one biopsy. Biopsies were classified into three categories according to predominant morphological features at low power magnification:
follicular lymphoma-like (n=7), progressive transformation of germinal center-like (n=22), and AITL-like features with follicular colonization (n=19).
Several cases have combinations of patterns. The neoplastic population is characterized by medium-sized cells with clear cytoplasm surrounded by IgD+ B-cells. Tumor cells are of helper T-cell immunophenotype [CD2+ (33/33 = 100%), CD3+ (45/48 = 93%), CD4+ (35/42 = 83%), CD5+ (39/39 = 100%), CD7+ (7/37 = 19%)], with frequent expression of CD10 (29/43 = 67%) and of TFH markers [PDCD-1 (32/36 = 88%), CXCL13+ (33/38 = 87%), BCL6+ (15/25 = 60%), CD57+ (9/16 = 56%)]. Scattered CD20+ B-immunoblasts (27/28 = 96%) and EBV+ cells (18/30 = 60%) are also frequently observed. Seven out of 31 patients (22%) in the 3 morphological patterns have t(5 ;9)(q33 ;q22) detected by fluorescent in situ hybridization. At prentation and/or at relapse, most patients had multiple lymphadenopathies (19/23 = 83%) and disseminated disease (stages III–IV, 22/28 = 79%). Skin lesions and B symptoms were present in 7/19 (37%) and 6/22 (27%) patients, respectively. In addition, 2 patients with sequential biopsies disclosed typical clinical & histopathological features of AITL in one episode. Our results show that this rare form of PTCL
has an immunophenotype indicative of TFH origin, is associated with t(5 ;9) in a proportion of cases, shows some similarities in morphology and immunophenotype with AITL, suggesting a relationship, and generates diagnostic pitfalls, especially with atypical reactive lymphoid lesions and some B-cell lymphomas.
The use of immunohistochemistry with TFH markers and molecular studies can help to make a correct diagnosis.