Risk Factors

An estimated 56,390 Americans were diagnosed with non-Hodgkin's lymphomas in 2005. For the past 25 years, the incidence in NHL has increased continuously. Most of this increase has been observed in people over 65. There is some evidence that the rates are now stabilizing or even declining.

Part of the reason for the dramatic rise is AIDS, which increases the risk for high-grade lymphomas. However, even after eliminating changes in diagnosing NHLs and known causes such as AIDS, there remains a 40% higher incidence over the past 40 years. The number of cases in which lymphomas first occur outside the lymph nodes has also increased compared to those limited to the nodes. (This observed increase, however, may in large part be due to different methods of diagnosing lymphomas).

Gender, Age, and Ethnicity

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The cancer can develop in people at all ages, including children, although is most common in those between the ages of 45 and 60. In general, the incidence of NHL is 50% higher in men than in women. This higher rate has been observed in many countries. Nevertheless, recent reports suggest that the rate is leveling off or even declining in men, but is increasing in women, particularly African American women. Overall, the risk is slightly higher in Caucasians than in African Americans.

A major 2000 study found that the risks for NHL among men versus women and among African Americans versus Caucasians may vary by lymphoma subtype. For example, follicular lymphomas were significantly higher in Caucasians than in African Americans and there was little gender difference. High-grade lymphomas were the most rapidly increasing type, particularly among men, with follicular lymphomas increasing most rapidly in African American men.