Nodal Peripheral T-cell Lymphoma with T Follicular Helper Phenotype Present CD20 Positive: A Case Report and Review of Literature

Background: T follicular helper cell is considered to be involved in B cell and a subset of effector T cell maturing. Nodal peripheral T-cell lymphoma with T-follicular helper phenotype (NPTCL-TFH) is a subset of peripheral T-cell lymphoma dened by expression of at least 2 or 3 TFH markers. Here we report a case of typical NPTCL-TFH while the B cell marker CD20 is positive. Case presentation: A 62-year-old male presented to our hospital with a symptom of dizzy and neck mass for 10 days. Physical examination and PET/CT revealed right cervical, armpit and inguinal lymphadenopathy, some of which were accompanied by pain. In the nodule biopsy, lymph node structure is destroyed, completely effaced by intermediate-sized monotonous lymphoid cells with round nuclei and abundant mitosis. Immunohistochemical staining conrmed that tumor cells were positive for T cell marker, and expressed several markers of TFH (CD4, Bcl-6, CXCL-13 and PD-1 ). Besides, in situ hybridization of EB virus showed scattered positive and TCR gamma arrangement is positive. However, with all these evidences of NPTCL-TFH, the tissue weirdly expressed CD20, a B lymphocyte maturing marker. The patient gave up treatment and unfortunately was died of tumor cachexia after 4-5 months. Conclusions: We report the rst case of CD20 positive in a NPTCL-TFH. More investigation and knowledge of this new phenotype need to be explored.


Background
Nodal peripheral T-cell lymphoma (NPTCL) is a rare type of lymphoma, accounts for about 7% of non-Hodgkin lymphoma (NHL) [1]. It has a broad morphologic spectrum with signi cant overlap to other lymphoma [2]. As for a new umbrella category of PTCL, nodal peripheral T-cell lymphoma with T-follicular helper phenotype (NPTCL-TFH) was rstly classi ed in the 2017 revision of the World Health Organization (WHO) classi cation of hematolymphoid neoplasms. Its characteristic feature is a predominant, dense, expanded interfollicular in ltrate of small-and medium-sized lymphoid cells admixed with a few large cells, possibly mimicking angioimmunoblastic T cell lymphoma(AITL) [3]. The difference between them is that TFH phenotype is de ned by expression of at least 2 or 3 TFH markers such as CD4, PD-1, CD10, BCL6, CXCL13, and ICOS [4,5]. CD20 is a well-known B lymphocyte-speci c membrane protein and is important in mounting optimal humoral immunity[6]. Its expression is associated with increased B cell signaling and T cell-dependent immune responses [7]. T-cell lymphoma rarely express CD20 unless there are special circumstances like T cell-independent immune responses [8,9]. So far there is no literature of CD20 expressed on NPTCL-TFH.
We report here a case of NPTCL-TFH with aberrant CD20 expression, hoping to provide cases and more cognition on this new type of peripheral T-cell lymphoma.

Case Presentation
The patient was a 62-year-old male who presented dizziness for 10 days without special cause. A week before admission, he found a mass on his right neck. Additional evaluation showed his right cervical, armpit and inguinal lymphadenopathy, some accompanied by pain. B symptom like fever, drenching night sweats, weight loss were not seen. The patient informed about smoking and drinking for 40 years, and his general medical history revealed no speci c surgery or disease. He also denies the family cancer history.
At the time of consultation, the patients' blood routine examination revealed that hemoglobin was 177 g/L, White blood cells, Platelets, Lactate dehydrogenase and Uric acid were within the reference range, no abnormality in other blood biochemistry tests was observed. Positron emission tomography / computed tomography (PET/CT) were applied to value multiple lymphadenopathies of the patient, including right jaw, bilateral cervical, right supraclavicular area, bilateral armpit, bilateral chest muscle, hilar, bilateral internal mammary, inferior vena cava on the diaphragm, etc. Result showed the size of the largest lymph node was about 3.4 centimeter in abdomen (Fig. 1). The shadow of swollen lymph node was round, cystic and low density.
Histological examination were made to gure out its properties. After the biopsy of the mass of his right neck, we got a pile of broken white tissue. Hematoxylin and eosin-stained sections showed the lymph node structure was destroyed, completely effaced by intermediate-sized monotonous lymphoid cells ( Fig. 2). Otherwise, atypical lymphocytes were medium in size, with irregular nuclei, some of which could be seen with nucleoli, and the cytoplasm of the cells was rich and lightly stained; a small number of cells were large in size and looked like immune maternal or central maternal; mitosis were easy to see. As for the cell background, there were no eosinophils, neutrophils or Reed-Sternberg-like cells. The blood vessels of the interstitium were obviously proliferated, but high endothelial venule(HEV) hyperplasia is not obvious. All of the features pointed to the haematopoietic and lymphoid tumor. Unlike angioimmunoblastic T-cell lymphoma, it did not show a prominent polymorphic in ammatory background, vascular proliferation, or expansion of follicular dendritic cell meshworks.
To gure out the diagnosis, we did immunohistochemical staining of a set of markers. The results suggest that T cell markers such as CD3, CD5, CD2 and CD4 were positive. Detection of CD7, CD8, ALK, CD30, CD10 were negative. What interest us is that, CD20, the marker often related with B cell maturing, also present positive here. But CD19, PAX-5, CD79a of whom suggest B-cell lymphoma were negative. IHC staining of this lymphoma sample con rmed CD4, Bcl-6, PD-1 and CXCL-13 positive. In the meantime, CD21 and CD23 clearly showed no follicular dendritic cell expansion, which support our diagnose of NPTCL-TFH. Additionally, tumore cells were negative for cyclinD1, IgD, MUM1, TdT, C-myc etc. Moreover, in situ hybridization reveals scattered positive EBER cells. The positive of clonal T-cell receptor (TCR) rearrangements further supported the diagnosis of T cell lymphoma. Analyze of IgH rearrangement is negative. In this regard, our nal diagnosis is peripheral T-cell lymphoma with T follicular helper phenotype (Fig. 3). Unfortunately, the patient gave up treatment for nancial reasons, and died of severe cancer cachexia 4-5 months after the biopsy. No autopsy was performed.

Discussion
T follicular helper cell (TFH) is a type of CD4 + helper T cell subset, located in the follicular germinal center to promote B cell expansion and differentiation [10]. The 2008 World Health Organization (WHO) Classi cation scheme broadly grouped PTCLs into Angioimmunoblastic T-cell lymphoma (AITL) and PTCL, not otherwise speci ed (NOS). At that time lymphoma of T follicular helper cell origin(TFH-NL) was belong to PTCL, NOS. However, the 2017 World Health Organization (WHO) Classi cation scheme turned to grouped PTCLs into TFH-NL and PTCL, NOS. Currently identi ed categories of T-follicular helper cellderived lymphomas include AITL, follicular T-cell lymphoma (FTL) (equivalent to the follicular variant of the original peripheral T), and NPTCL-TFH [1,11]. The diagnostic criteria of NPTCL-TFH are: a) shared immunophenotypic features with AITL; b) expressed at least 2(ideally 3) TFH markers; c) lack of In ammatory/polymorphous background; d) few HEV proliferation; e) no follicular dendritic cell(FDC) meshwork expansion [12]. In a review by Parwiz J et al., T-and NK-cell lymphomas comprise only about 6% of all lymphoproliferative disorders, and the most frequent type is the not otherwise speci ed (NOS) category [13], NPTCL-TFH only account for less than 1% of all T-cell neoplasms [14,15], therefore our case is very rare. Although our case is not the rst NPTCL-TFH case reported, we rstly found CD20 expressed in this disease. All of the morphologic features, immunohistochemical results, scattered EBV + cells and Tcell arrangement positive proved our case to be a NPTCL-TFH. What interest us is CD20 get strong staining on the tissue. As a recognized B cell marker, CD20 is less well positive on T cells.  [17]. Recently there were more cases observed in NPTCL [18,19], however we report the very rst case presented CD20 positive in NPTCL-TFH after 2017 WHO Classi cation scheme. CD20 positivity in T-cell lymphomas may include derivation from subsets of CD20 positive T-cells undergoing neoplastic transformation or CD20-acquisition following neoplastic transformation of the T-cells [19]. We suppose that T-follicular helper cells may have a supporting effect on B cells in the germinal center, and thus differentiate into CD20-expressing cells. Or TFH cells have uncertain direction of differentiation of progenitor B cells. [20] NPTCL-TFH should be distinguished from other types of peripheral T cell lymphomas, especially AITL.
The clinical difference between AITL and NPTCL-TFH remains unclear, for they both have the symptoms of multiple lymphadenopathies, splenomegaly, B symptoms, hypergammaglobulinemia, eosinophilia, or a positive Coombs test [14]. In regards of pathology, AITL are disorganized and show a diffuse polymorphous in ltrate that includes a variable proportion of medium-sized neoplastic T cells with abundant clear cytoplasm. these common characteristics in morphology often messed up with NPTCL-TFH, only through immunohistochemistry and molecular features can separate them [21][22][23]. With the new criteria, about 70% AITL can be rede ned as NPTCL-TFH [21,22]. AITL and TFH-NPTCL, may represent a morphologic continuum is further strengthened by the reported observations of transitions from one diagnosis to the other [2,12,23]. Our case's morphological feature is similar to AITL, but the exact expression of CD4, Bcl-6, PD-1 and CXCL-13, scattered EBV positive cells and the T cell receptor arrangement positive proved it T follicular helper cell phenotype.
PTCL-NOS is another rare T-cell lymphoma needing to be distinguished. As the most common subtype of mature T cell lymphoma, it is a diagnosis of exclusion. There is no particular morphological aspect of this tumor [24]. The lymph node often consists of numerous medium-sized or large cells with irregular, pleomorphic, hyperchromatic, or vesicular nuclei. Clear cells and Reed-Sternberg-like cells can also be seen. Unlike PTCL-TFH, PTCL-NOS has a very important in ammatory background in morphology, while hyperplasia of high endothelial venules and/or follicular dendritic cells are not usually seen [1]. Although our case displays similar cell feature with PTCL-NOS, it does not have a prominent polymorphic in ammatory background, and the expression of TFH markers instead of CD30, a possible marker of PTCL-NOS also supports our diagnosis.
Moreover, follicular T cell lymphoma (FTCL) has some similar features with PTCL-TFH, because they both derived from T follicular helper cells. Sang Eun Yoon et al. classi ed 207 cases diagnosed with nodal lymphomas of T follicular helper (Tfh) cell origin into 111 cases of AITL, 68 cases of PTCL-NOS, 19 cases of FTCL and 10 cases of PTCL-TFH phenotype, but they cannot analyze FTCL and PTCL-TFH as different diseases with immunolabeling [25]. In FTCL, two distinct growth patterns are recognized: one that mimics follicular lymphoma and one that mimics progressive transformation of germinal canters [14]. The interfollicular areas lack the polymorphic in ltrates and vascular proliferation characteristic of AITL [26]. Our case shows no FDC expansion on CD21, which highlights the diagnose is not FTCL.
We did the immunohistochemical labeling of CD30 and ALK was to make a differential diagnosis with anaplastic large cell lymphoma(ALCL). ALCL can be divided into ALK-positive and ALK-negative subtypes based on expression of ALK or ALK gene rearrangement [1]. The neoplastic cells were mainly medium to large size with moderate basophilic cytoplasm, which mimics with our case. However, most of them had hyperchromatic nuclei and prominent nucleoli [27]. So added the negative expression of CD30 and ALK, we eliminate the consideration of ALCL.
Since some of the tumor cells were CD20 positive, we should not ignore some B-cell neoplasms such as Hodgkin lymphoma, High-grade B-cell lymphoma. It's just that the positive T cell markers and TCR rearrangement in our case con rmed that it was derived from T cells. Mantle T-cell lymphoma or other non-Hodgkin lymphomas such as Hepatosplenic T-cell lymphoma, Primary cutaneous anaplastic lymphoma, Primary cutaneous peripheral T-cell lymphomas also have some distinguishment points in our case. However, in general, it's the molecular feature, expression of Bcl-6, CD4, PD-1 and CXCL-13 and positive of TCR arrangement that con rms our diagnose.

Conclusions
More and more cases will be recognized with the growing knowledge of NPTCL-TFH. To do this correct diagnosis, we need to be aware that before diagnose a PTCL-NOS or AITL, use T follicular cell markers to eliminate NPTCL-TFH. Although very rare, CD20 can occur in NPTCL-TFH, exhaustive molecular and phenotypic investigations should be performed to get further understanding.