In this study, we investigated particularities of nasal and nasal-type ENKTL diagnosed in Tunisia, a non-endemic region, during a 15-year period. ENKTL is a rare lymphoma subtype of peripheral T/NK cell lymphoma with a variable incidence according to geographical region. ENKTL were more frequently reported in Asia and Latin America [3]. Indeed, ENKTL accounts for 12.9–25% of all non-Hodgkin’s lymphomas in China, Thailand, and Singapore [3, 11]. Europe and North America were less affected [12]. In Tunisia, ENKTL remains an exceptional tumor since only nine cases were reported during the study period.
ENKTL mainly occur in the fourth and fifth decades, with a mean age of 50 years [13]. In our series, the patient mean age was 48 years. In Asian series, the patients were younger than in the Western series [14]. Pediatric ENKTL remains exceptional [15, 16]. Although few series found a female preponderance, male predominance has been reported by several series with a male-to-female ratio ranging from 2 to 4.5 [1, 13]. Interestingly, herein, we observed a large male predominance.
The nasal ENKTL are localized in the nasal cavities, paranasal sinuses as well as the cavum, tonsils, hypopharynx, and larynx [17]. Nasal ENKTL are characterized by progressive-stage ulceronecrotic lesions in the medial structures of the face, preferentially in the nasal fossae and the sinuses [17]. Nasal ENKTL can also develop in the Waldeyer’s ring, oral cavity, and hypopharynx. The nasopharynx has been rarely involved [18]. In our series, NKTL were diagnosed in the nasal cavity (five cases), the soft palate, and the sub-mandibular gland. In addition, nasal-type ENKTL may involve the skin, soft tissues, testes, gastrointestinal tract, bone marrow, liver, and upper respiratory tract [17]. However, tracheal and laryngeal localizations were rare [19]. Herein, we reported two nasal-type ENKTL involving the skin and the soft tissue.
According to the Ann-Arbor classification, early clinical stage ENKTL were the most commonly diagnosed forms at the time of diagnosis with approximately two thirds of patients having localized disease in the nasal cavity or adjacent sites [14, 17]. However, other reports described either only early clinical stages [13] or mainly metastatic stages [18]. In our series, ENKTL were diagnosed predominantly in early stage (six cases), the remaining two cases were diagnosed at disseminating stages.
The histopathological diagnosis is particularly difficult, because of the frequent entanglement of infected and necrotic-inflammatory phenomena with lymphoid proliferation. Hence, the biopsy must be performed at a distance from the necrosis. T/NK cell lymphoma showed polymorphic lymphoid proliferation, consisting of small, medium, and large cells, with atypical irregularly contoured nuclei [18]. The tumor proliferation is most often associated with a polymorphic inflammatory infiltrate made of lymphocytes, eosinophilic polynuclear cells, plasma cells, and histiocytes. Ischemic necrosis was frequently observed and associated with lesions of angiocentrism [17].
The differential diagnoses of T/NK lymphoma are mainly the Wegener’s disease and bacterial and fungal infections. Nevertheless, IHC remains essential to establish the diagnosis [17]. As ENKTL develops from cytotoxic cells, mainly NK cells and more rarely T cells, they exhibit intracytoplasmic CD3 expression as well as CD2 and CD56 expression [17, 18, 20]. However, less than 5% of T lymphocytes and a small proportion of NOS lymphomas can express CD56 [18]. Although the significance of the expression of this adhesion molecule remains unknown, CD56-positive lymphomas are characterized by an extranodal invasion, a high aggressivity, and a poor prognosis [21]. Herein, six ENKTL expressed CD56.
NK/T lymphomas are most often CD4−/CD8−, more rarely CD4−/CD8+ [17]. In our study, CD4 was negative in all cases and CD8 was expressed in three ENKTL. CD57 can be expressed [22]. NK/T lymphomas usually have an activated cytotoxic phenotype, expressing the cytotoxic granule-associated proteins, such as T1A, Granzyme B, and Perforine [17]. In the current study, the expression of Granzyme B was detected in eight ENKTL. Moreover, there is a strong correlation between the expression of CD56 and that of Granzyme B.
During the last decade, EBV detection by ISH and IHC demonstrated the association of ENKTL with EBV infection, regardless of ethnic and geographical distribution [8, 23]. Using novel techniques, such as DNA microarrays, array comparative genomic hybridization, and “next-generation” sequencing, the oncogenesis of EBV-associated NK/T lymphomas are now being clarified, although the exact molecular mechanisms remain unresolved [23,24,25]. Overall, among immunocompetent patients, EBV-infected cells are most frequently reported in NK/T lymphomas and angioimmunoblastic T lymphomas than in B lymphomas, suggesting an important role of this virus in the pathogenesis of these lymphomas [23, 24]. Interestingly, herein, all ENKTL were EBER-positive similar to Northern Chinese patients [18]. Takada et al. showed recently that EBV induces NF-κB-mediated survival signals in T and NK cells, contributing to the lymphomagenesis of these cells [26].
The optimal treatment of ENKTL remains poorly established due to the rarity of this lymphoma and the small sample size of the randomized controlled trials. Studies have clearly shown that the clinical response to chemotherapy in localized forms is unfavorable, since a complete response is observed in only 40 to 60% of patients [1]. In our study, patient 2 died due to bone marrow failure 4 months after diagnosis and patient 8 had bone marrow failure and died after meningeal relapse. Radiation therapy followed by or in combination with chemotherapy is the best initial treatment since it improves the local control of the disease and reduces the local and systemic recurrence [17, 18, 21]. However, it has not been well-established whether this association can provide a benefit for survival. Most studies have shown that conventional chemotherapy followed by radiotherapy seems to be ineffective for the majority of patients [1, 23]. As a result, it has been suggested that current chemotherapy protocols should be reserved for the control of micro-metastases following radiotherapy [1]. Herein, the radio-chemotherapy combination was indicated in five patients, and the median survival of this group of patients was longer than that of the exclusive multi-chemotherapy group (5 years 8 months versus 1 month 15 days).
Since nasal-type ENKTL is an aggressive and persistent disease, conventional chemotherapy is insufficient for the eradication of this lymphoma. Some studies have suggested that high-dose chemotherapy, supported by stem cell transplantation, with a combination of an l-asparginase-based regimen can significantly improve the “anti-tumor effect” and eventually overcome drug resistance [17, 27]. In a prospective study of 29 newly diagnosed nasal ENKTL, after two to three courses of the SMILE protocol, 24 cases showed a response rate of 86% with a complete response obtained in 69% of patients [27]. l-Asparginase as a single agent is effective in treating recurrent or treatment-resistant ENKTL [27, 28]. Nevertheless, in our study, only one patient received SMILE protocol and died, in a context of meningeal relapse, complicated of febrile pancytopenia. Although this worse outcome, SMILE regimen remains the current standard of care in many countries for ENKTL patients of diverse age groups and performance status, with newly diagnosed or relapsed/refractory tumors and in early to advanced stages [27].
Post-treatment surveillance of ENKTL patients should be clinical, biological, and radiological. The quantification of the circulating copy rate of the EBV DNA by polymerase chain reaction technique is a predictive parameter of relapse or recurrence of this lymphoma [17, 29]. The prognosis overall remains poor with a median survival of only 13 months [7, 13]. The estimated 5-year overall survival is between 40 and 50% [12]. Survival is heavily dependent on stage at diagnosis. Patients with an early clinical stage have higher 5-year survival rates regardless of the type of treatment received. This rate is even lower for advanced stages not exceeding 10% [12]. In our study, the evolution was favorable in only four cases in which a complete response was obtained (patients 1, 4, 6, and 7) of which three cases were classified at early clinical stages.
Similar to other EBV-associated cancer, novel immunotherapy options targeting LMP1 protein may improve clinical outcomes for ENKTL patient [30]. In two clinical trials of EBV-cytotoxic T lymphocytes as an adjuvant therapy, durable responses were observed [17].
