During immunosuppression, which, in combination with a latent EBV infection, is the main pathophysiological mechanism for EBV-MCU development, the immunosurveillance by cytotoxic T cells is reduced, and the virus can enter lytic replication again. While the virus can be kept in a dormant state systemically, localised EBV-driven lymphoproliferations can appear.
Histopathologically, EBV-MCU is a sharply circumscribed ulcer that is characterised by a polymorphous infiltrate of EBV-positive atypical immunoblasts, which range in size, and other inflammatory cells, such as lymphocytes, plasma cells, eosinophils and histocytes [
1]. The atypical immunoblasts show a Hodgkin and Reed–Sternberg (HRS) cell-like morphology, which is difficult to distinguish from those present in classical Hodgkin lymphoma. Presenting a B-cell immunophenotype, these HRS-like cells express CD20, CD30, MUM1, PAX5, OCT-2, CD79a, BOB1 and, in about half of the cases, CD15. A clonal rearrangement of the immunoglobulin genes might be observed, indicating clonal out growths of the EBV-positive B cells. A small rim of surrounding T-lymphocytes can be commonly found. These T cells are mainly CD8-positive and often show a monoclonal or clonal restriction of T-cell receptor (TCR) gene rearrangements, leading to a limited repertoire against EBV epitopes [
1]. Furthermore, apoptotic cells and necrosis can be detected as well.
2. EBV-MCU and Haematologic Malignancies
EBV-MCU usually appears because of a medically induced immunosuppression or because of advanced-age-associated immunosenescence. Beside the age, which is seen as a co-factor, immunodeficiency in our patient was mainly caused by a relapsing chronic lymphatic leukaemia. CLL was mentioned to be one of the most common haematologic malignancies known to produce immune defects independent of therapy [
56]. The histopathologic and immunohistochemical features of the ulcers of the pharynx and the lower lip showed the characteristic pattern of an EBV-MCU with a B-cell polymorphous infiltrate, including HRS-like cells and an expression for CD20 and CD30, and also showed areas consistent with simultaneous CLL/SLL infiltration. Thus, the manifestation of the CLL/SLL, clearly presented in the lymph node biopsy, was also detectable in both ulcers. The simultaneous manifestation of an EBV-MCU and another malignant disorder within the same lesion had not been described in the literature before.
There are few described cases of a synchronous or metachronous appearance of EBV-MCU and different lymphoproliferative diseases [
13,
16,
22,
56], with only three cases occurring in association with a present haematologic malignancy [
37,
41,
56].
Khazal et al. reported on a 75-year-old male patient with a medical history of CLL many years earlier that had been treated with rituximab, fludarabine and cyclophosphamide as well as recurrent left arm Merkel cell carcinoma that was treated by radiation therapy, surgery and pembrolizumab [
37]. He presented with a painful gingival ulcer with progress to mandibular infiltration that fit the histological characteristics of an EBV-MCU. A bone marrow evaluation showed 60–70% CLL infiltration. Although the large HRS-like cells within the ulcer biopsy raised the possibility of a Hodgkin-type Richter transformation of the CLL, the diagnosis was finally based on clinical presentation and course.
The second case described a 29-year-old adult with intermediate-risk acute T-cell lymphoblastic leukaemia (T-ALL) who was treated with Children’s Oncology Group protocol AALL0434 chemotherapy, including methotrexate and mercaptopurine, at the time of left-sided throat pain caused by an exudative left palatine tonsillar ulcer [
41]. The biopsy of the ulcer showed a polymorphous infiltrate of lymphocytes, neutrophils, plasma cells and histiocytes as well as HRS-like cells. These cells were positive for CD20, CD30, CD45 and EBER and were negative for CD5, CD10 and CD15, which was, all in all, consistent with the diagnosis of an EBV-MCU. As in the previous case, there were no simultaneous histological signs of the T-ALL within the ulcer. After the EBV-MCU did not regress despite a reduction of the immunosuppressive drug therapy, a single dose of rituximab (375 mg/m
2) was administered and the ulcer resolved within two weeks.
Pina-Oviedo et al. analysed the clinical and pathological features of patients who developed a lymphoproliferative disorder after a therapy for a haematologic malignancy [
32]. One of these patients, an 82-year-old woman with CLL under treatment with fludarabine, cyclophosphamide and rituximab, developed an EBV-MCU at the base of the tongue. Histopathology and immunohistochemistry were typical for EBV-MCU, with cells positive for CD20, CD30, CD45/LCA, CD79a, PAX5, OCT2 and EBER and negative for CD3, CD15 and BOB1. Thus, unlike our case, no infiltration by the CLL was noted. Three months later, she developed cervical lymph nodes that were infiltrated by an EBV-positive diffuse large B-cell lymphoma (DLBCL) and died. While DLBCL was the most common type of LPD after cancer therapy, the primary haematologic malignancy among this study group was predominantly CLL, assuming a certain predisposition for developing an EBV-positive lymphoproliferative disorder (EBV + LPD).
3. EBV-MCU and Other LPDs, a Challenge of Differentiation
EBV-MCU shares morphologic and phenotypic characteristics with more aggressive forms of lymphoproliferative disorders, such as EBV-positive diffuse large B-cell lymphoma (DLBCL), classic Hodgkin lymphoma (cHL), post-transplant lymphoproliferative disorder (PTLD), plasmablastic lymphoma (PBL), anaplastic large cell lymphoma (ALCL) or lymphomatoid granulomatosis (LyG), which sometimes makes it extremely difficult to distinguish.
4. EBV-Positive Diffuse Large B-Cell Lymphoma (DLBCL)
EBV-positive diffuse large B-cell lymphoma (DLBCL) is a high-grade lymphoma with a poor outcome. It presents a wide range of morphological features, from polymorphous infiltrates of HRS-like cells, immunoblasts and plasma cells in an inflammatory background of histiocytes and lymphocytes with areas of prominent necrosis and angioinvasion to a T-cell-like or more monomorphic pattern [
39]. The cells are positive for CD20, CD19, CD79a, PAX5, OCT2, BOB1, MUM1 and CD30, with variable co-expression of CD15. CD10 is mostly negative and CD45 and BCL6 show a variable expression. There is a widespread positivity for EBER. These almost indistinguishable similarities to EBV-MCU, cHL may be misleading and all clinical, histologic, and immunohistochemical features must be considered to avoid misdiagnosis [
14]. Both diseases predominantly occur in elderly people with presumed immunosenescence, but while EBV-MCU shows a localised nature and often a self-limiting course, DLBCL occurs as a generalised, extranodal progressive disease. The sharply circumscribed EBV-MCU with a small rim of T cells at the base can be differentiated from the more infiltrative pattern in DLBCL. Considering the findings of Ohata et al., a mutational panel and the absence of CD10 and BCL6 expression in EBV-MCU can be supportive [
55].
Furthermore, Satou et al. observed that, in contrast to DLBCL and cHL, immune evasion via the programmed cell death protein 1/programmed cell death 1 ligand 1 (PD1/PD-L1) pathway is usually absent in EBV-MCU [
18]. However, Daroontum et al. reported a case of a PD-L1-positive EBV-MCU in a patient with multiple EBV-driven lymphoproliferative B-cell disorders [
45]. All lesions had PD-L1 expression in the EBV-positive large B cells and HRS-like cells, but there was evidence for a clonal relationship among these lesions by PCR analysis for IGH. The majority of DLBCL show clonal IGH and restricted or oligoclonal TCR rearrangements because of a reduced T-cell repertoire [
1]. EBV DNA serum levels often correlate with the burden of disease [
39].
The clinical presentation of EBV-MCU, with its strictly localised occurrence and the absence of mass lesions, is crucial in distinguishing these two entities [
10,
14,
16]. There are some reports of lesions that were initially diagnosed as DLBCL before being reclassified as EBV-MCU [
9], and, therefore, special attention should be drawn to their similarity.
5. Classic Hodgkin Lymphoma (cHL)
Classic Hodgkin lymphoma (cHL) is one of the most common lymphoma types worldwide. It is associated with a non-obligatory presence of EBV infection and most commonly leads to an impressive cervical and mediastinal lymphadenopathy. Patients are often presenting B symptoms. cHL shares some (immune)histological characteristics with EBV-MCU, especially the presence of CD30-positive HRS cells co-expressing CD15 in a strong inflammatory background. These cells are also positive for MUM1. The tumour cells show a downregulation of B-cell markers and transcription factors such as OCT2 and BOB1, with a remaining slight expression of PAX5, whereas EBV MCU more often expresses CD 20 [
10,
14].
In EBV-associated cHL, typically only the HRS cells are positive in EBER in situ hybridization, which is an important fact regarding the differentiation to EBV-MCU in which EBER positivity can be detected in several different cell types. In addition, EBV MCU displays an EBV latency type III with expression of the Epstein–Barr virus nuclear antigen 2 (EBNA 2), whereas cHL presents latency type 0/I or II and is negative for EBNA 2. At least HRS cells express PD-L1 ligands and consistently express LMP1 that starts the NF-kappa B and JAK/STAT signalling pathway, leading to proliferation [
10,
14]. Applying to this entity as well as for the DLBCL, the clinical presentation of the EBV MCU with strict localised and superficial occurrence is crucial in differentiating these two entities [
10].
6. Plasmablastic Lymphoma (PBL)
Another important EBV-associated LPD that also mainly occurs in the oral cavity is the plasmablastic lymphoma (PBL), a highly aggressive form of non-Hodgkin lymphoma (NHL) with an immunophenotype of terminally differentiated B cells and a loss of typical B-cell antigen expression. The large plasmablasts lack CD20, CD19, CD45 and PAX5 and show an expression of plasma cell markers that are positive for CD79a, MUM1, CD38 and CD138 [
12,
14]. The cells show an overall expression of MYC protein, and the proliferation rate is high (Ki-67). Most cases are EBV-positive in the EBER in situ hybridization. The PBL is associated with immunosuppression, mainly due to HIV infections, and its localisation in the head and neck region makes it important as a potential differential diagnosis of EBV-MCU. Beside the immunohistochemical differences, PBL shows a monomorphous pattern with sheets of plasmablasts, whereas the EBV-MCU is characterised by a typical polymorphous pattern [
9,
12]. In contrast to the benign course of EBV-MCU, the prognosis of PBL is poor, with high observed mortality rates.
7. Post-Transplant Lymphoproliferative Disorder (PTLD)
Post-transplant lymphoproliferative disorder (PTLD) is an immunodeficiency-related proliferation of B cells that are latently infected with EBV after solid organ transplantation and is another important disease to consider in the differential diagnosis of EBV-MCU [
7]. The symptoms are nonspecific and can be like those in infectious mononucleosis. PTLD can form tumour masses that may obstruct organs or spread further, leading to organ dysfunctions. The monoclonal form has an especially aggressive course. The histological features contain the full range of B-cell maturation, from immunoblasts to plasma cells and variable-sized lymphocytes. The HRS-like cells are positive for CD20 and CD30, while CD15 has been reported to be negative. There is an expression of LMP1, inducing an uncontrolled cell proliferation. EBER is mainly positive for EBV. Blood levels of EBV DNA measured by PCR have been shown to predict the development of PTLD [
31]. Hart et al. detected EBV DNA in the blood of patients with solid organ transplantation in about 80% of all cases, presenting a quantifiable EBV viremia [
7,
31]. This viremia usually does not present in patients with EBV-MCU and, therefore, can be a further distinguishing feature [
17,
21,
59]. Nevertheless, the presence of EBV DNA in the blood does not automatically exclude the diagnosis of EBV-MCU [
9]. EBV DNA and antibody levels in the blood of patients with EBV-MCU has not been regularly measured and should be further investigated. EBV MCU can arise with typical clinical presentation and corresponding histomorphology in the background of immunodeficiency caused within the post-transplant setting. In those cases, no formal differential diagnosis is necessary, but the lesion should be reported as polymorphous PTLD with features of an EBV-MCU [
10].
8. Anaplastic Large Cell Lymphoma (ALCL)
Anaplastic large cell lymphoma (ALCL) is a type of NHL with the presence of large pleomorphic cells that are positive for CD30 and is another differential diagnosis of EBV-MCU due to histological similarities. It typically presents at a late stage with systemic symptoms as a general lymphadenopathy, extranodal disease or as a cutaneous ulcer. A rare subtype can occur after breast implant reconstruction. The cells are negative for CD3 and for EBV in the EBER in situ hybridization [
17,
63].
9. Lymphomatoid Granulomatosis (LyG)
Lymphomatoid granulomatosis (LyG) is an EBV-driven B-cell LPD that is associated with immunosuppression with angiodestructive features and is characterised by a cell infiltrate of small T cells and variable numbers of large atypical immunoblasts and HRS-like cells that are positive for CD20, CD30, LMP1 and EBER but not usually for CD15. The differentiation to EBV-MCU merely relies in the clinical presentation with lung lesions or affliction of the central nervous system [
33].
10. Head and Neck EBV-MCU Management
Beside all these histological similarities to other lymphoproliferative disorders, EBV-MCU predominantly occurs in the mucosa of the oral cavity and the oropharynx and, therefore, mimics squamous cell carcinomas at first sight. As these two entities can clinically present in a similar morphology and the treatment of each is completely different, it is very important to take an early biopsy to exclude an oral or oropharyngeal squamous cell carcinoma. Of course, this also applies to ulcerative lesions of the skin in the head and neck region, as with the ulcer of the lower lip in our patient.
As EBV-MCU is still a rare entity of lymphoproliferative disorders, it is important to mind it as a potential disease in elderly and immunocompromised patients with persistent cutaneous or mucosal ulcerative lesions. An early biopsy must be taken to distinguish it from other malignant disorders. Imaging, a blood examination, including EBV serology, and, in some uncertain cases, a bone marrow biopsy can be helpful to exclude a systemic lymphoproliferative disorder.
Since the awareness for EBV-MCU is currently still low and ulcerative lesions can be easily misdiagnosed, there might be cases of unnecessary patient overtreatment [
8]. Due to the limited experiences, no consensus or formal guideline for EBV-MCU treatment exist, and therapeutic strategies are only based on case reports and literature reviews.
If possible, immunosuppressive drug therapy should be reduced or discontinued as a first step. Conservative treatment is possible if the ulcer remains localised. In persistent or progressive cases, rituximab monotherapy (375 mg/m
3, four weekly doses) or as a part of a chemotherapy (R-CHOP) should be considered. Local radiation had a beneficial effect in destructive courses. The selection of the appropriate therapy should be made in regard to clinical and individual aspects. However, in accordance with Hujoel et al., a lack of response within three months should always lead to another biopsy to re-evaluate the diagnosis of EBV-MCU [
57].