Extranodal NK/T-cell lymphoma, nasal type, is a well-defined cytotoxic lymphoma . This lymphoma is commonly located in the upper respiratory tract, especially the nasal cavity, but involvement of other organs can be observed, particularly the skin. The disease may be primary cutaneous: that is, staging investigations can be negative at presentation [2,8,33,34]. This lymphoma is not recognized in the EORTC classification where, depending on the size of neoplastic cells, cases would be classified as CD30- large T-cell lymphomas or small- to medium-sized pleomorphic T-cell lymphomas . The WHO classification recognizes extranodal NK/T-cell lymphoma, nasal type, as a distinct entity . The dis ease is more common in particular areas such as Asia, Mexico, and Central and South America.
In the past, similar cases were reported as 'lethal midline granuloma' or 'granuloma gangrenescens' [36-39]. Over many years, it has become recognized that lethal midline granuloma is a term encompassing various diseases with different aetiologies and pathogeneses, and that the majority of cases are associated with EBV, have a lymphoid differentiation and an aggressive course [40-44]. Lethal midline granuloma represents direct extension of the lymphoma from the nasal cavity to the overlying skin, with destruction of the bone and soft tissues. Some cases of extranodal NK/T-cell lymphoma, nasal type, were also included in the groups of angiocentric lymphoma and polymorphic reticulosis [6,45,46].
As for all lymphomas listed in this chapter, overlapping clinicopathological features are common and classification can be arbitrary. Most cases have an NK phenotype and are associated with EBV infection . Negativity for T-cell markers and germline rearrangement of T lymphocytes, together with positivity for EBV in neoplastic cells, should be interpreted as a strong hint towards a diagnosis of extranodal NK/T-cell lymphoma, nasal type.
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