No abstract

It is well known that extranodal NK/T-cell lymphoma (NK/TCL) nasal type clusters in Asian countries. A large series of 78 cases of nasal NK/TCL from Peru is analyzed in the present study. Two histologic groups 1 (monomorphic) and 2 (polymorphic), were segregated according to the proportion of large cells (above and below 30%, respectively). Catalyzed signal amplification technique was performed for enhancement of immunohistochemistry reactivities. Epstein-Barr virus (EBV) sequences and types were investigated using polymerase chain reaction. Clinical characteristics, stage, outcome, and response to treatment were evaluated in both groups. Fourteen cases (18%) and 64 cases (82%) corresponded to groups 1 and 2, respectively. Except for nasal obstruction, more common in group 2, all other symptoms were similar in both groups. Local extension and staging were also comparable. Both groups showed CD3c+ CD2+ CD56+ CD3s- CD20- immunophenotype. All cases were positive for EBV. In this series type-2 EBV was found more frequent than type-1 EBV, contrarily to that observed in Asian series. However, about one-third of cases simultaneously harbored both viral types. Both groups received an average of 50-Gy dose of radiation therapy (RT), with or without chemotherapy. Complete therapeutic response was achieved in 89% of group 1 and in 74% of group 2, but this difference was not statistically significant. There were no significant differences between the groups regarding disease-free survival, failure-free survival, relapse, and overall survival. The overall survival, in both groups, was longer for patients treated with RT alone compared with those treated with combined RT therapy and chemotherapy. The present study has shown that dividing nasal NK/TCL in monomorphic and polymorphic variants, according to frequency of large cells, does not correlate with clinical and prognostic factors.

We have described 5 major subtypes of Epstein-Barr virus (EBV) based on variations in EBNA-1 sequences. These include P-ala (identical to the prototype B95.8 virus), P-thr, V-pro, V-leu, and V-val. Normal individuals often carry multiple EBV subtypes, the most common being P-ala, whereas EBV-associated tumors examined to date always contain a single subtype, which only on rare occasion is P-ala. The primary hypotheses that these observations generate are as follows: (1) Each of these EBV subtypes are naturally occurring, and in normal individuals the multiplicity of subtypes results from multiple infections. (2) EBV subtypes in normal individuals are generated in vivo from a single infecting virus subtype by mutations in EBNA-1. The second hypothesis essentially excludes the possibilities that the nonrandom association of certain subtypes with lymphomas is secondary to the geographic distribution of EBV subtypes and, if proven correct, could provide strong support for a direct role of EBV in tumorigenesis. In this report, we provide evidence for the latter hypothesis. We show that the P-ala EBV subtype present in most nasal lymphomas undergoes and accumulates multiple mutations consistent with the generation of variant species of EBNA-1 in vivo. This phenomenon is similar to the generation of quasispecies in RNA viruses and is the first description of in vivo generation of subtypes in DNA viruses. In RNA-based viruses, including human immunodeficiency virus and hepatitis C virus, the emergence of quasispecies is linked to replication infidelity and significantly influences disease processes through its effect on viral tropism, the emergence of viruses resistant to the host defenses or to therapy, and pathogenicity. The present data thus raise important questions relating to the mechanisms whereby these mutations are generated in EBV and their relevance to the pathogenicity of EBV-associated lymphomas.