Epidemiology of non-Hodgkin lymphoma.

Non-Hodgkin Lymphoma (NHL) occurs worldwide although there is notable geographical variation in incidence and subtype distribution. These differences are due to a combination of demographic, environmental and other unidentified factors. A dramatic increase in NHL incidence was seen starting around 1970, with subsequent stabilization 10 years ago. Despite this plateau, the number of new cases in many countries will increase significantly in coming years due primarily to aging populations. In the majority of cases, strong risk factors are not identifiable. There is significant epidemiological heterogeneity between NHL subtypes, yet cancer registries have tended to consider NHL as a single entity. This is one of several epidemiological obstacles discussed.