Increasing Incidence of Non-Hodgkin's Lymphoma in Canada, 1970-1996: Age-period-cohort Analysis

Previous studies have shown that the incidence of non-Hodgkin's lymphoma (NHL) has increased in many parts of the world in recent decades. Using data obtained from the Canadian Cancer Registry, the present study examined time trends in NHL incidence in Canada between 1970 and 1996 and the effects of age, period of diagnosis and birth cohort on incidence patterns for each sex separately. Results showed that overall age-adjusted incidence rates increased substantially, from 7.3 and 5.2 per 100,000 in 1970-1971 to 14.0 and 10.0 per 100,000 in 1995-1996 in males and females, respectively. Diffuse lymphoma was the major histological subtype, accounting for approximately 76% of NHL cases over the 27-year period. The data suggest that period effects have played a major role, although birth cohort effects may also have been involved. Sex-specific patterns of the incidence were similar over the time period of diagnosis but were distinct among recent birth cohorts. In conclusion, there is in fact a marked increase in NHL in Canada which cannot be explained in terms of improvements in diagnosis, changes in NHL classification and the increase in AIDS-associated NHL alone. The birth cohort effect in NHL suggests that changes in risk factors may have contributed to the observed increase.