Introduction

Nasal natural killer (NK)/T-cell lymphoma, formerly known as "lethal midline granuloma" or "polymorphic reticulosis," is an extranodal tumor of NK-cell origin, with a predilection for the nasal cavity (35). Extranodal NK/T-cell lymphomas and LYG have been referred to as angiocentric immunoproliferative lesions, but further studies have revealed that the two diseases have different clinical features and immunophenotypes. They should therefore be considered distinct entities (Table 3). LYG is an Epstein-Barr-virus (EBV)-positive B-cell proliferative disease with a secondary T-cell response, whereas nasal NK/T-cell lymphoma is an EBV-positive NK cell or cytotoxic T-cell disorder. LYG, unlike nasal NK/T-cell lymphoma, frequently involves the lung, kidney, and CNS, and rarely the nasal area. Similarities between the two diseases include EBV positivity and histologic features (necrosis and angiocentric damage) (36). The report of the Hong Kong Workshop on Nasal and Related Extranodal Angiocentric T/NK Cell Lymphomas stated that nasal NK/T-cell lymphoma should be considered a distinct clinical-pathological entity based on its biologic behavior, characteristic immunophenotype, and strong association with EBV (37). Nasaltype NK/T-cell lymphoma is now recognized as a distinct lymphoma subtype within the

TABLE 3 EBV-Positive Extranodal Angiocentric Immunoproliferative Diseases

Disease

Sites of involvement

Phenotype

Comments

Nasal-type NK/T-cell

Nasal cavity Paranasal sinuses

NK/T-cell

Radiation may be helpful to control localized nasal disease

Subcutaneous tissue

GI tract

Testis

Poor response to chemotherapy

Skin

Kidney

GI tract

Liver

B-cell

Variable clinical course: from indolent with spontaneous remission to very aggressive lymphoma

Abbreviations: CNS, central nervous system; EBV, Epstein-Barr virus; GI, gastrointestinal; LYG, lymphomatoid granulomatosis; NK, natural killer.

Abbreviations: CNS, central nervous system; EBV, Epstein-Barr virus; GI, gastrointestinal; LYG, lymphomatoid granulomatosis; NK, natural killer.

World Health Organization classification of lymphoid tumors and includes both nasal and extranasal tumors (38).

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