Extranodal NK/T-cell lymphoma 時間: 2011-01-27 12:53:02
Extranodal NK/T-cell lymphoma
Introduction
Extranodal NK/T-cell lymphomas have a broad cytologic spectrum and are characterized by frequent necrosis, angiocentric growth, cytotoxic immunophenotype, and a strong association with Epstein-Barr virus (EBV).1 Extranodal NK/T-cell lymphomas, nasal type is used to further describe this lymphoma and actually includes the lymphoma that occurs in the upper aerodigestive tract, including nasal cavity, nasopharynx, oral cavity, oropharynx and hypopharynx. The nasal cavity is the prototypic site in the first description of the disease.1,2 In a recently published series, 60% to 90% of cases are localized in the nasal and upper aerodigestive region. A more recent study found that 68% of extranodal NK/T-cell lymphomas are derived from the nasal cavity and 26% are from extranasal sites.3
Extranodal NK/T-cell lymphoma is uncommon and occurs often among Asians and among Mexicans and South Americans of Native American ethnic origin, accounting for approximately 6% of all non-Hodgkin’s lymphomas in these populations, compared with less than 1.5% in Western populations.4-7 This lymphoma affects adults almost exclusively with a wide range of ages (14-78 years of age) and the median age is 52 and 45 years for nasal and extranasal type, respectively. The male-to-female ratio is 2:1.3
EBV appears to play an important etiologic role in the genesis of extranodal NK/T-cell lymphomas. EBV association is seen in almost all cases of nasal NK/T-cell lymphoma (90% to 100% of reported cases) and in some reports expression of EBV early RNA (EBER) was an obligatory inclusion criterion for extranodal NK/T-cell lymphomas, irrespective of the patients’ ethnic origins.3,4,8,9 NK/T-cell lymphoma extranasal type is also strongly associated with EBV in Asian patients, but some cases in Caucasian patients have been EBV-negative. EBER has also been found with extranodal NK/T-cell lymphomas in the patients following renal transplantation, indicating that iatrogenic immunosuppression with EBV infection may facilitate the development of this lymphoma.11,12
Clinical Features
Nasal NK/T-cell Lymphoma
Nasal NK/T-cell lymphomas arise in the nasal cavity and nasopharynx, causing progressive destructive and ulcerative lesions (so-called midfacial destructive disease, lethal midline granuloma, and polymorphic reticulosis) or obstructive symptoms due to mass lesions. The neoplasm frequently spreads to the adjacent anatomic structures in the upper aerodigestive tract such as the paranasal sinus, orbit, oral cavity, palate, oropharynx, and hypopharynx , and is typically associated with bone erosion.13 Most patients have early-stage disease (about 70%-85% stage I and II) at presentation.3,13 Bone marrow is involved in approximately 10% of patients at presentation. The involvement requires CD56 immunohistochemistry and/or EBER in situ hybridization to confirm, although CD56 also stains plasma cells and osteoblasts.3 An additional 10%-20% develop marrow involvement during the course of the disease.
Extranasal NK/T-Cell Lymphoma
Extranasal NK/T-cell lymphoma is less common than the nasal type.3,7 The most frequently involved sites are the skin, gastrointestinal tract, bone marrow, testis, lung, orbit, central nervous system, adrenal gland, and soft tissues; these are the same sites to which nasal NK/T-cell lymphoma tends to disseminate during the course of the disease.3,7,8,9-24 Patients often present with late-stage disease (stage III or IV), with involvement of multiple anatomic sites (55% showed >2 extranodal sites involved).8,13 Systemic symptoms such as fever, malaise, and weight loss are common. Serum lactate dehydrogenase is often elevated, and anemia is not uncommon.3 The performance status is often poor.3 Skin lesions take the form of multiple nodules or plaques, which commonly ulcerate with a necrotic center. Intestinal lesions often manifest as perforation, attributable to the prominent tissue necrosis. Involvement of the testis, CNS, or soft tissue usually manifests as mass lesions.9-24
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Morphology
The histological features of extranodal NK/T-cell lymphoma are similar irrespective of the site of involvement. Mucosal locations often show extensive ulceration (Fig. 1). Zonal geographic and coagulative necrosis and admixed apoptotic bodies are common, comprising ghost shadows of necrotic cells and karyorrhectic debris admixed with fibrinoid exudate and blood. The lymphomatous infiltrates are diffuse and permeative. The cytologic spectrum of extranodal NK/T-cell lymphoma is broad. The neoplastic cells may be small, medium-sized cells, or large, but the most common is medium-sized lymphoma cells admixed with small and large neoplastic cells. The small cells usually have irregularly folded, angulated, or serpentine nuclei with dense chromatin, inconspicuous nucleoli, and a narrow to moderate rim of pale cytoplasm. Sometimes the small neoplastic cells are indistinguishable from normal small lymphocytes.25 The medium-sized cells possess round or irregularly folded nuclei, granular chromatin, small nucleoli, and a moderate amount of pale to clear cytoplasm (Fig. 2). The large cells have round or folded nuclei, vesicular or granular chromatin, and distinct nucleoli (Fig. 3). Occasionally the large cells appear anaplastic. Mitotic figures are easily found, even in small cell-predominant lymphomas. Apoptotic bodies are frequently interspersed among the lymphoma cells and are sometimes ingested by tingible body macrophages. Angiocentric growth, defined as accentuation of tumor cells around blood vessels, with infiltration and destruction of vessel wall (Fig. 4),1,26 is reported in 25% to 100% of cases.7 Even in the absence of lymphoma infiltration, the blood vessels commonly show fibrinoid necrosis, fragmentation of the elastic lamina, and thrombosis. The necrosis and vascular damage are reminiscent of those observed in other EBV-associated lymphoproliferative disorders such as Burkitt’s lymphoma and lymphomatoid granulomatosis. These features have been postulated to be mediated by EBV-induced monokines and chemokines, such as the monokine induced by interferon-γ and the interferon-γ-inducible protein-10.27
Extranodal NK/T-cell lymphoma, particularly those predominated by small or mixed cell populations, or those accompanied by a heavy admixture of inflammatory cells, including small lymphocytes, plasma cells, histiocytes and eosinophils may mimic an inflammatory process (Fig. 5).7,28 The lymphoma can sometimes be accompanied by florid pseudoepitheliomatous hyperplasia of the overlying epithelium, mimicking well differentiated squamous cell carcinoma (Fig. 6).1
Site-Specific Features
In the upper respiratory tract the mucosal glands are often pushed apart and destroyed by the lymphoma cells. Some mucosal glands can exhibit cytoplasmic clearing due to cell injury. The surface epithelium can be infiltrated by lymphoma cells or, uncommonly, undergoes squamous metaplasia and florid pseudoepitheliomatous hyperplasia, with irregular downgrowth of squamous epithelium and nuclear atypia, mimicking well differentiated squamous cell carcinoma.1
In the skin there is a perivascular, periadnexal, or diffuse infiltrate of lymphoma cells in the mid and deep dermis, with or without subcutaneous involvement. Coagulative necrosis and ulceration are common. Invasion of the epithelial structures is more frequently seen in nasal NK/T-cell lymphoma disseminating to skin than in primary cutaneous NK/T-cell lymphoma.29 In the subcutaneous tissue the lymphoma cells infiltrate among the adipocytes, producing a panniculitis-like picture (Fig. 7). The lymphoma cells can rim around fat vacuoles, and fat necrosis is common.8 The histologic features may be indistinguishable from subcutaneous panniculitis-like T-cell lymphoma.
In the gastrointestinal tract there is usually transmural infiltration by lymphoma cells. Extensive coagulative necrosis, deep ulcers, and perforation are common.8,22,30
In the testis there is a dense interstitial infiltration by lymphoma cells, often accompanied by angiodestruction and necrosis.14 The seminiferous tubules are lost, atrophic, or infiltrated by lymphoma cells.
In the soft tissues a permeative growth of tumor cells with prominent destruction of skeletal muscle fibers and invasion of the nerves is seen. Sometimes the muscle fibers show flocculent necrosis, invasion of the cytoplasm by lymphoma cells, or dropout of individual cells, leaving empty spaces.21

Immunophenotype
The prototypic immunophenotype of NK/T-cell lymphoma is CD2+ (Fig. 8), surface CD3-, cytoplasmic CD3ε+ (Fig. 9), and CD56+ (Fig. 10), although occasional cases may show minor deviations, such as lack of cytoplasmic CD3ε or CD56 expression.1,28 CD43 and CD45RO are commonly positive. Other T-cell-associated antigens such as CD4, CD5, CD7 (Fig. 11), CD8, TCRαβ, and TCRγδ are usually negative.1,3,28 Very commonly, only paraffin-embedded material is available for a biopsy suspected of NK/T-cell lymphoma. Therefore, immunohistochemistry studies on paraffin-embedded material are the method of choice to diagnose this disease.
Normal mature NK cells express CD16, CD56 (almost all), and CD57 (~70%).32 However, in extranodal NK/T-cell lymphoma the only NK marker consistently expressed is CD56; CD16 and CD57 are almost always negative.1 In most cases, the expression of CD56 is consistent in the various sites of involvement and in relapses with a variation of staining intensity and percentage. In some cases a CD56+ tumor may relapse as a CD56- tumor, or vice versa. It should be emphasized that CD56 expression is not entirely specific for NK/T-cell lymphoma. It is also expressed in some cases of peripheral T-cell lymphomas (particularly those expressing TCRγδ), acute myeloid leukemia, myeloma, small cell neuroendocrine carcinoma, rhabdomyosarcoma, and some other tumors. Thus, a diagnosis of extranodal NK/T-cell lymphoma should not be based on CD56 expression alone. It should be supplemented by positive immunostaining with other markers (e.g., CD3ε, CD2, cytotoxic granules markers).
Cytotoxic molecules such as T-cell intracellular antigen I (TIA-1), granzyme B, and perforin are usually positive,1,33 and they may mediate the tissue injury and cell death commonly observed in this lymphoma.34
CD30 is positive in about half of the cases, especially in those rich in large cells.1,3,10 In contrast to anaplastic large cell lymphoma, CD30 expression is usually focal and not intense.1,3,10
The proliferative fraction as demonstrated by Ki-67 immunostaining is usually high (>50%).3,35 Studies have suggested that a high Ki-67 index is associated with a worse prognosis for extranodal NK/T-cell lymphoma.3,35 Some cases can exhibit aberrant expression of CD20.28,31 The significance of CD20 aberrant expression in extranodal NK/T-cell lymphoma is still unclear.28
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EBV detection
There is a strong association between EBV and the occurrence of extranodal NK/T-cell lymphoma. Virtually all lymphoma cells in extranodal NK/T-cell lymphoma are positive for EBER (Fig. 12).1 Although some EBV- cases have been reported, this phenomenon may be related to differences in criteria for case inclusion.7 For example, in the recent International Peripheral T-Cell Lymphoma Project study, EBV positivity was an obligatory inclusion criterion.3 It is prudent to require EBV positivity for confirmation of diagnosis in extranasal cases, because many types of peripheral T-cell lymphomas show morphologic and immunophenotypic overlap with NK/T-cell lymphoma.
The EBV is present in a clonal episomal form with type II latency pattern (EBNA-1+, EBNA-2+, LMP-1+) and commonly shows a 30-base pair deletion in the latent membrane protein-1 gene. This is probably the reason that immunostaining for EBV LMP-1 is often weak or negative and thus should not be relied on for demonstrating EBV in this lymphoma. In fact, the most sensitive method for demonstrating EBV in extranodal NK/T-cell lymphoma is in situ hybridization for EBER. PCR for EBV is highly sensitive but is of limited value because even the presence of rare bystander EBV+ lymphocytes can produce a positive result due to its ultrasensitivity. Therefore, in situ hybridization for EBER is the most reliable test for demonstration of the presence of EBV infection for this type of lymphoma.1 Circulating plasma or serum EBV DNA levels are often elevated, and a high titer is correlated with extensive disease, unfavorable response to treatment, and poor survival.
Pearls and pitfalls in immunophenotypic diagnosis of extranodal NK/T-cell lymphoma in paraffin-embedded tissue
In the nasal cavity or nasopharynx, a presumptive diagnosis of extranodal NK/T-cell lymphoma can be made based on a cytoplasmic CD3ε+, CD56+ phenotype, together with a compatible morphology, because lymphomas in this location with this immunophenotype are almost always extranodal NK/T-cell lymphomas. Negative staining for CD5 or CD7 gives additional support for the diagnosis. If nasal lymphoma is negative for CD56, it is essential to demonstrate the presence of both cytotoxic markers and EBV to render a diagnosis of nasal NK/T-cell lymphoma. Some of these cases are probably NK-cell lymphomas that have lost CD56 expression, whereas others are cytotoxic T-cell lymphomas, as evidenced by surface CD3 expression. Some of the latter express TCRαβ and some express TCRγδ.36 Nasal lymphomas that show a CD3ε+, CD56-, cytotoxic molecule-positive, EBV- phenotype are not included in this category and should be diagnosed as peripheral T-cell lymphoma, not otherwise specified. The clinical features and morphology of the CD56- group are indistinguishable from those of the CD56+ group.3,28
In extranasal sites, a mere cytoplasmic CD3ε+, CD56+ immunophenotype is not sufficient to support a diagnosis of extranodal NK/T-cell lymphoma because many different lymphomas can exhibit a similar phenotype, such as peripheral T-cell lymphoma with TCRγδ expression, type II enteropathy-associated T-cell lymphoma, and primary cutaneous gamma-delta T-cell lymphoma. Additional studies are required to support the diagnosis of extranodal NK/T-cell lymphoma, including lack of CD5 expression, lack of βF1 expression, positive EBER in situ hybridization, and lack of TCR gene rearrangement using PCR. Demonstration of T-cell origin does not preclude a diagnosis of extranodal NK/T-cell lymphoma as long as other features are typical. However, classification of tumors that lack expression of CD56 and cytotoxic granule-associated protein (TIA-1, granzyme B, and perforin), but EBER is positive and occur in the nasal area remains problematic.28 2008 WHO classification requires both EBV positivity and cytotoxic granule protein expression for a diagnosis of extranodal NK/T-cell lymphoma.1
Genetics and Molecular Findings
The TCR and immunoglobulin genes are in germline configuration in the majority of cases. A small proportion of cases shows rearrangement of the TCR genes–up to 38% for nasal cases and 27% for extranasal cases in one series.3 The positive cases probably represent neoplasms of cytotoxic T-cells rather than NK cells.3,7, 37,38
Complex chromosomal abnormalities have been found in extranodal NK/T-cell lymphomas.1 The most common changes are 6q-, 2q+, 8p-, 11q-, 12q-,
13q-, 15q+, 17q+, and 22q+. Specific chromosomal translocations have not been identified, but translocations involving the 8p23 breakpoint have been reported in a number of cases.39,40
Overexpression of p53 protein occurs in 45% to 86% of NK/T-cell lymphomas, whereas p53 gene mutation is found in 24% to 62% of cases, with some variation in frequencies reported from different populations.41,42 The p53 mutation has been found to correlate with large cell morphology and advanced stage at presentation.43,44 Mutations of the β-catenin, K-Ras, and c-Kit genes are detected in 22%, 14%, and 6%, respectively, but the significance is not clear.43
Differential Diagnosis
Herpes simplex infection of the nasopharynx can stimulate a reactive lymphoid proliferation and mimic nasal NK/T-cell lymphoma due to a mass lesion and an extensive lymphoid infiltrate with necrosis. In addition, the lymphoid cells are predominantly CD56 positive but lack cytotoxic markers.45 Also the presence of scattered herpes virus inclusions, lack of angioinvasion, expression of CD4 by the T-cell infiltrate, absence of EBV, and lack of TCR gene rearrangement rule out a diagnosis of NK/T-cell lymphoma.45
The surface epithelium of mucosa can undergo squamous metaplasia and florid pseudoepitheliomatous hyperplasia, with irregular downgrowth of squamous epithelium and nuclear atypia, mimicking well differentiated squamous cell carcinoma.1 Therefore, squamous carcinoma should be in the differential diagnosis. In extranodal NK/T-cell lymphoma, nasal type, there is no deep invasion by the proliferative squamous mucosa. Desmoplastic reaction or carcinoma in situ components are not seen.
Wegener’s granulomatosis is an important differential diagnosis for nasal NK/T-cell lymphoma. It is a much more common destructive lesion of the upper respiratory tract in Western countries. It shares many morphologic features with the nasal NK/T-cell lymphoma in the form of a mixed inflammatory infiltrate, ulceration, necrosis, and vasculitis or vasculitis-like lesions. It also involves the kidney and lung and shows granuloma formation with multinucleated giant-cells. Serum antineutrophil cytoplasmic antibody is positive and EBV is negative. These should distinguish Wegener’s granulomatosis from nasal NK/T-cell lymphoma.
Lymphomatoid granulomatosis (LYG) shares a number of features with extranodal NK/T-cell lymphoma, nasal type, and extranasal type, including its association with EBV and propensity for necrosis and vascular damage.46,47 Indeed, it is likely that the presence of EBV plays a major role in producing these pathologic similarities. Based on these features, both LYG and extranodal NK/T-cell lymphomas were sometimes referred to as angiocentric lymphomas or angiocentric immunoproliferative lesions.48 However, further studies clarified the nature of these conditions and revealed that LYG is an EBV-positive B-cell proliferation associated with an exuberant T-cell reaction (a peculiar form of T-cell-rich large B-cell lymphoproliferative disorder with a strong association with EBV) rather than a T-cell or NK cell lymphoproliferative disorder.49 Therefore, the distinction is based on the immunophenotype and genotype of the EBV-positive cells, B cell versus NK cell.50
Extranodal NK/T-cell lymphoma arising in the skin, with no evidence of sinonasal involvement, usually has a differential diagnosis of pleomorphic/transformed mycosis fungoides, peripheral T-cell lymphoma (PTCL), NOS, blastic plasmacytoid dendritic cell neoplasm (CD4+/CD56+ hematodermic malignancy), or subcutaneous panniculitis-like T-cell lymphoma.28 Mycosis fungoides is different in that the tumor is positive for CD4, CD5, and negative for cytotoxic granule proteins and EBV. PTCL, NOS can be CD56+, but usually is negative for EBV and cytotoxic granule proteins. Blastic plasmacytoid dendritic cell neoplasm shows monotonous medium-sized blasts-appearing tumor cells with round to oval nuclei, fine nuclear chromatin, thin nuclear membrane and a small rim of cytoplasm. They are usually CD4+, CD56+, CD123+, TdT+/- and CD3ε-. No EBV is involved. Subcutaneous panniculitis-like T-cell lymphoma usually demonstrates surface CD3 and CD8 positivity. There is no overexpression of CD56 or EBV infection by tumor cells.1
Cases arising in the small intestine with or without involvement of the adjacent lymph nodes have a differential diagnosis with enteropathy-associated T-cell lymphoma (EATL), type I and II. Type I EATL shows no CD56 expression, but type II is positive for CD56. However, the patient usually has a history of refractory celiac disease; EBV and cytotoxic granule proteins are negative.1 Atypical proliferation of NK cells producing superficial erosions of the gastrointestinal tract has been reported in a patient with antigliadin antibodies but the absence of full-blown celiac disease.51 These lesions are relatively circumscribed and superficial, and the CD56+ NK cells are negative for EBER. The benign nature of the disease is further confirmed by the nonprogressive course and improvement with a gluten-free diet.51
Cases of extranodal NK/T-cell lymphoma with predominantly large tumor cells should be distinguished from diffuse large B-cell lymphoma (DLBCL) in the upper aerodigestive tract. DLBCL is CD3ε- and CD20+. A study found that lymphomas involving the sinuses without nasal involvement were predominantly DLBCL, whereas lymphomas involving the nasal cavity alone were extranodal NK/T-cell lymphoma, nasal type.52
Clinical Course
NK/T-cell lymphoma, nasal type mostly presents with localized disease. However, dissemination to various sites frequently occurs either early or late in the course of the disease.53,54 Hemophagocytic syndrome may complicate the disease in some patients.55 Radiotherapy is the conventional initial treatment for patients with localized stage I-II nasal NK-cell lymphomas.
The response rate ranges from 60%-80%, complete remission rate from 40%-80%, and median 5-year OS from 40%-59%. However, about half of all patients will relapse.56
Systemic failure occurs in 25-30% of patients, suggesting that many apparently stage I-II patients have disseminated disease at diagnosis. Therefore, for medically-fit patients, chemotherapy should be an integral part of treatment even if radiotherapy is given first.
For stage I-II nasal NK-cell lymphomas, primary chemotherapy gives a complete remission rate of 40-60%.56 However, disease progression during chemotherapy occurs in 30-40% of patients, necessitating the use of salvage radiotherapy. Furthermore, up to 30-40% of patients relapse after complete remission.56 This high failure rate has been attributed to the expression of the multidrug resistance (MDR) gene in NK-cells, which is recapitulated in neoplastic NK-cells.57 For stage III-IV nasal tumours, non-nasal tumours of any stage, chemotherapy is the only option. Anthracyclin-based regimens such as CHOP (cyclophosphamide, hydroxydaunomycin, Oncovin [vincristine], prednisone) have traditionally been used, but the results are disappointing,3,53 and complete remission rates for chemotherapy of stage III-IV nasal and non-nasal tumours are less than 15%.56 Combined chemotherapy and radiotherapy is an attractive option for stage I-II nasal lymphomas. Radiotherapy should be administered early. Six cycles of chemotherapy, with radiotherapy delivered after the first three courses, is the current standard for stage I-II nasal NK-cell lymphoma.58 Early radiotherapy is beneficial, so concurrent chemotherapy and radiotherapy is preferred to chemotherapy followed by radiotherapy.56 A recent pilot study of the combination of L-asparaginase with P-glycoprotein in dependent drugs including prednisolone, methotrexate, ifosfamide and etoposide (SMILE), has also shown promising results in patients with advanced-stage or refractory NK/T-cell malignancies.59 L-asparaginase-containing regimens are currently the most promising chemotherapy for relapsed and refractory NK-cell lymphoma, although their role in frontline treatment remains to be defined.
Since around 50-70% of patients with NK-cell lymphoma will relapse after complete remission and marrow involvement is uncommon, the autologous or allogeneic stem cell support (HSCT) is a possible approach. However, the reported survival benefit requires further confirmation.56
Monitoring patients after treatment and assessment of posttreatment biopsies of nasal NK/T-cell lymphoma
In nasal NK/T-cell lymphoma, chronic infection due to tumor obstruction or irradiation-induced mucosal damage often results in thickening of the linings of the nasal cavity and paranasal sinuses, making it difficult to assess CT or MRI for persistent disease. PET-CT provides a functional and anatomical assessment of disease status, and is the preferred radiological follow-up investigation.60,61 Patients who fail to achieve undetectable circulating EBV DNA, or those with a rise in EBV DNA exceeding that at presentation, have a worse prognosis. Furthermore, patients in apparent complete remission with persistently raised circulating EBV DNA will invariably relapse, and are therefore candidates for additional therapy.62 Prospective EBV DNA quantification is routinely done in centers specialized in NK-cell lymphoma.62
Because the nasal cavity is readily accessible, it is fairly common practice to take posttreatment biopsy specimens from that location in patients with nasal NK/T-cell lymphoma to determine whether there is residual lymphoma. Atypical lymphoid residual tumor is easy to recognize if the lymphoma is made up of predominantly large cells or if dense sheets of cells are evident. In most cases, the mucosa becomes hypocellular. Scattered residual lymphoma cells hiding among normal small lymphocytes or residual lymphomas consisting of small cells are very difficult, if not impossible, to recognize by morphologic assessment alone. Therefore, it is prudent to routinely perform immunostaining for CD56 and in situ hybridization for EBER to look for residual tumor cells. Positive cells must be present at least in aggregates or correlated with atypical cytology to be considered indicative of residual lymphoma. The presence of only isolated cells or groups of three to four positive cells has to be considered inconclusive, because low numbers of positive cells can be observed in the normal nasal or nasopharyngeal mucosa. With relapse, the cytologic features of the original lymphoma are usually maintained; however, they may sometimes change from small or medium-sized cells to large cells, or vice versa. Occasionally CD56 expression is diminished or even lost in treated or relapsed lymphoma.