Epidemiology of non-Hodgkin's lymphoma (NHL): trends, geographic distribution, and etiology.

While for most cancers incidence and mortality are decreasing, those of non-Hodgkin's lymphoma (NHL) are steadily increasing. Research to define reasons for this increase is extensive, but has not yet resolved them. We have conducted a literature analysis on trends regarding changes in the incidence, geographic distribution, and etiologic factors of NHL. From our own and previous analyses, an increasing NHL incidence at a rate of 3-4% per year was observed for the 1970s and 1980s. This stabilized in the 1990s, nevertheless still with an annual rise of 1-2%, resulting in almost a doubling of the NHL incidence. This rise has been noted worldwide, particularly in elderly persons >55 years. Concerning gender subgroups, a male predominance throughout all age groups is apparent. Although the NHL incidence has historically been higher in whites than blacks, disproportional increases have recently been observed in the latter group. Increases in high-grade NHL and extranodal disease are predominant. Differences in geographic distribution are striking for follicular lymphoma, which is more common in Western countries than elsewhere. Asians have higher rates of aggressive NHL, T-cell lymphomas, and extranodal disease. In the Middle East, high rates of intestinal extranodal disease are observed, whereas in Africa, endemic Burkitt's lymphoma accounts for a substantial proportion. Risks for developing NHL include immunosuppression and a causal link between infectious agents, and lymphomagenesis has also been determined, particularly for human T-cell leukemia/lymphoma virus type 1 (HTLV-1), Epstein-Barr virus (EBV), and Helicobacter pylori infections. Exposure to environmental agents and occupational risks have been studied; however, their significance is as yet uncertain.