NK-cell related neoplasms in Osaka, Japan.

The frequency of NK-cell related neoplasms was estimated among lymphoproliferative diseases diagnosed and treated in Osaka, Japan, from 1999 to 2003. The total number of registered cases was 1,400, among which 1,092 patients were diagnosed as having malignant lymphomas. There were 987 cases of non-Hodgkin's lymphoma (NHL) and 105 (9.6%) of Hodgkin's lymphoma. Immunophenotypic analysis revealed that 743 patients had B-cell lymphomas and 209 T/NK-cell lymphomas. Among the T/NK-cell lymphomas, 40 showed positive immunoreactivity for CD56, and thus they were judged to be NK/T-cell lymphomas. They included one blastic NK-cell lymphoma and 39 NK/T-cell lymphomas. NK/T-cell lymphomas were further divided into three categories based on the main site of lesions: nasal type (23 cases), non-nasal extranodal type (11 cases), and nodal type (5 cases). The positive rate of infection with the Epstein-Barr virus determined by in situ hybridization was 83%, 36%, and 25% in the nasal, non-nasal, and nodal type, respectively. A mosquito allergy was found in one patient with EBV-positive non-nasal NK/T-cell lymphoma. The present study showed that the frequency of NK-cell related neoplasms among all NHLs was 4% in an ATL-non-endemic area of Japan.