Plasmacytoma of the gastrointestinal tract in Korea: higher incidence than in Japan and Epstein-Barr virus association.

As a result of a systematic review of non-Hodgkin's lymphoma of the gastrointestinal tract (GI) at the Yonsei University, Seoul, Korea and the Osaka University, Osaka, Japan, we found an extramedullary plasmacytoma in 5 of a total of 78 cases (6.4%) in Korea and 1 of 136 cases (0.7%) in Osaka, which represents an approximately 9-fold difference in frequency. The presence of the Epstein-Barr virus (EBV) genome was examined in paraffin-embedded specimens from the 5 cases with GI plasmacytoma from Korea together with 17 patients collected by a nationwide study in Japan. There were no clinical findings suggestive of the presence of immunodeficiency in these Korean and Japanese patients. There were no prominent differences in the age distribution or sex ratio between the patients of the two countries. Histologically, the proliferation of mature plasma cells was almost monomorphous with occasional bi- or multinucleated forms. The immunohistochemistry revealed a restricted cytoplasmic expression of immunoglobulin light chain, kappa type in 8 cases and lambda type in 14. A polymerase chain reaction of preserved DNA from 4 Korean and 16 Japanese patients found that only 2, both Korean, were positive for EBV of subtype A. The difference in the frequency of EBV positivity between Korean and Japanese cases was significant (p < 0.05). In situ hybridization revealed positive signals in the nucleus of the tumor cells. IHC revealed that the tumor cells in these two cases were positive for latent membrane protein-1 and EB nuclear antigen-2, showing latent infection of EBV. These findings suggest a close association of EBV and Korean GI plasmacytoma, and might partly explain the remarkable number of cases in this country.