Sinonasal NK/T-cell lymphomas in the United States

Sinonasal natural killer (NK)/T-cell lymphomas are common in Asia and areas of South and Central America but are rarely seen in the United States, whe re they have not been as well characterized. Fifteen cases diagnosed in Sou thern California were studied with respect to histologic features, immunoph enotype, Epstein-Barr virus EBER in-situ hybridization (EBV EBER-ISH), and T-cell receptor gamma chain (TCR-gamma) gene rearrangement. Although ethnic background was available for only seven patients, six were of Asian or His panic descent with only one non-Hispanic white known. Twelve presented as s inonasal lesions, but three were limited to the oropharynx. Most cases (11 of 15) demonstrated both necrosis and an angiodestructive pattern. All case s demonstrated cytoplasmic CD3 positivity (15 of 15), and were positive for both TIA-I and granzyme B (14 of 14). Perforin was positive in 5 of 14. CD 56 was expressed in 10 of 15 and CD8 in 3 of 15. EBV EBER-ISH was positive in 13 of 14 and TCR-gamma gene rearrangement was detected in 1 of 14 cases. None (0 of 14) were positive for CD16 or CD57. Although CD16-positive hist iocytes were abundant, double-label EBER-ISH/IHC failed to identify CD16 ex pression on EBV-positive tumor cells. Three cases with pleomorphic large ce ll morphology showed focal CD30 positivity, raising the differential diagno sis of anaplastic large cell lymphoma, but all were ALK-1-negative and othe rwise similar to the other cases of NK/T-cell lymphoma. Sinonasal NWT-cell lymphomas in the United Stares most often occur in ethnic soups from areas of reported high frequency (Asia, Central and South America), although less commonly than in endemic populations, and are otherwise similar phenotypic ally. A combined approach, including immunohistochemistry, EBV EBER-ISH, an d TCR gene rearrangement studies, is most helpful to arrive at the correct diagnosis.