REPORT OF THE WORKSHOP ON NASAL AND RELATED EXTRANODAL ANGIOCENTRIC TNATURAL-KILLER-CELL LYMPHOMAS - DEFINITIONS, DIFFERENTIAL-DIAGNOSIS, AND EPIDEMIOLOGY

A workshop jointly sponsored by the University of Hong Kong and the So ciety for Hematopathology explored the definition, differential diagno sis, and epidemiology of angiocentric lymphomas presenting in the nose and other extranodal sites. The participants concluded that nasal T/ natural killer (NK) cell lymphoma is a distinct clinicopathologic enti ty highly associated with Epstein-Barr virus (EBV). In situ hybridizat ion for EBV can be very valuable in early diagnosis, especially if tis sue is sparse. The cytologic spectrum is broad, ranging from small or medium-sized cells to large transformed cells. Histologic progression often occurs with time. Necrosis is nearly always present, and angioin vasion by tumor cells is seen in most cases. Nasal T/NK cell lymphoma has a characteristic immunophenotype: CD2-positive, CD56-positive, but usually negative for surface CD3. Cytoplasmic CD3 can be detected in paraffin sections. Clonal T-cell receptor gene rearrangement is not fo und. Tumors with an identical phenotype and genotype occur in other ex tranodal sites, most commonly in the skin, subcutis, and gastrointesti nal tract, and should be referred to as nasal-type T/NK cell lymphomas . The differential diagnosis includes lymphomatoid granulomatosis, bla stic or monomorphic NK cell lymphoma/leukemia, CD56-positive periphera l T-cell lymphoma, and enteropathy-associated T-cell lymphoma.