Epidemiology of mature T-cell and NK-cell neoplasms: east and west.

Mature T-cell and natural killer (NK) cell lymphomas are uncommon. Their epidemiological data are mainly derived from Western and Eastern countries, some with significant variations. These differences may be related to genetic susceptibilities, prevalence of oncogenic viruses and other environmental factors. Nodal mature T-cell lymphomas are most common, with their incidences varying ethnically/geographically. Extranodal T-cell lymphomas have very different epidemiologic features. Adult T-cell leukaemia/lymphoma, due to human T-cell leukaemia virus type-1 (HTLV-1) infection, is found mainly in HTLV-1 endemic areas. Mycosis fungoides, the most common cutaneous T-cell lymphoma in the West, accounts for <2% of T-cell lymphomas in Asia. Epstein-Barr virus (EBV) related T-cell lymphomas are common in Asia and Central/South America but exceptional in the West. Germline polymorphisms of HLA-DPB1, IL18RAP and HLA-DRB1 genes have been defined in Chinese NK/T-cell lymphoma patients, potentially affecting susceptibility to EBV-related lymphomagenesis. This review explores these epidemiological differences and how they may impact on management.