Epidemiology of the non-Hodgkin's lymphomas: Distributions of the major subtypes differ by geographic locations

Background: There has been no previous systematic study of the distribution of the major subtypes of non-Hodgkin's lymphoma (NHL) across geographic regions, although there have been isolated reports of such differences. Design: As part of a clinical evaluation of the International Lymphoma Study Group (ILSG) classification of NHL, we classified 1378 NHLs from eight different geographic sites (Omaha, NE, USA; Vancouver, BC, Canada; Capetown, South Africa; London, England; Wurzburg/Gottingen, Germany; Lyon, France; Locarno/Bellinzona, Switzerland; and Hong Kong) using the ILSG classification. Results: Substantial differences were found in the distribution of the major subtypes of NHL across geographic regions (P < 0.0001). A greater percentage of follicular lymphoma was seen in North America, London and Capetown (31% versus 14% at other sites). Peripheral T-cell lymphoma was more common in London. Capetown and Hong Kong (9%) than elsewhere (3%). In Locarno/Bellinzona, higher percentages of mediastinal large B-cell lymphoma (9% versus 2% elsewhere) and mantle cell lymphoma (14% versus 6% elsewhere) were seen. Angiocentric nasal T-/NK-cell lymphoma was only seen in Hong Kong (8%) and Lyon (2%). Conclusions: Our study provides evidence that the distribution of NHL subtypes differs by geographic region. These findings suggest that geographical differences in etiologic or host factors may be responsible for the observed differences in the distribution of cases across NHL subtypes.