Epidemic of Non-Hodgkin Lymphoma in New Zealand Remains Unexplained

Background. Non-Hodgkin lymphoma (NHL) incidence rates have increased considerably in New Zealand. Methods. Incidence and mortality rates for NHL from 1981 to 2010 were calculated. Trends in age-specific rates were analysed and age-period-cohort models fitted to explore generation-specific changes in incidence and mortality. Results. NHL incidence increased by 67% for men and 74% for women between the 1981–1985 and 2006–2010 time periods in New Zealand. For women born about 1936 and men born about 1946, NHL incidence and mortality have diverged suggesting an improved prognosis for recent generations. Conclusion. The strong generation effects suggest that an exposure before 25 years of age is of major importance in determining the lifetime risk of NHL in New Zealand. NHL incidence rates in New Zealand will continue to increase in the future and probably more in females than males, as generations with increased risk age. Current hypotheses for the cause of NHL do not explain the trends observed. A decline in the prevalence of a protective factor may have also contributed to these trends. Examination of trends for subtypes of NHL and innovative testable hypotheses that may explain these trends are needed.