ABSTRACT
The international adoption of the World Health Organization classification of lymphoid malignancies has provided a common framework to compare subtype-specific lymphoma epidemiology at the country level and on a worldwide scale. The site at which lymphoma cells proliferate is probably a reflection of an interaction between tumor cell characteristics and growth-promoting microenvironmental features. Genetic factors associated with ancient populational migration from Asia to the American continent over the Aleutian range may explain the similarities between Asian and native American populations with regard to the epidemiology of natural killer (NK)/T-cell lymphoma of nasal type. Extranodal NK/T-cell lymphoma, nasal type, and Enteropathy-type T-cell lymphoma are entities with an epidemiology suggestive of an underlying genetic susceptibility that probably plays an important role in the pathogenetic process. The primary organ of origin may influence the outcome, and the presence of two or more extranodal sites is currently used as an adverse prognostic factor in the International Prognostic Index for aggressive lymphomas.
