Cancer incidence among Iranian immigrants in Sweden and Iranian residents compared to the native Swedish population

Abstract

Background and goals Comparing cancer incidence by migrant studies is one of the main approaches to generate hypotheses on the aetiology of cancer. Immigrant studies are most informative when cancer incidence data are available from both the source and the host country. Methods The age standardised incidence rate (ASR) and standardised incidence ratio (SIR) of cancers among the Iranian immigrants were compared to the native Swedish population as the standard population by using the Swedish Family-Cancer Database (FCD) from 1958 to 2006. We also compared SIRs between Iranian immigrants and Iranian residents for whom the data were derived from the Iranian national cancer registry report of 2006. Results Among the 65,501 Iranian immigrants, the median age at immigration was 26 years and the median length of stay was 16 years. Their all-cancer ASR was 175.3 and 153.1 per 100,000 person years for males and females, respectively, during the period from 1996 to 2006, higher than for the Iranian residents. The ASRs increased among the male Iranian immigrants during the past two decades but were stable among females. The risk for all-cancers among Iranian immigrants was lower than that for the native Swedish population. The Iranian immigrants had a significantly increased risk for male urinary bladder (SIR = 1.40) and thyroid cancers (2.64) compared to the Swedes. Conclusion The reasons for the decreased risk for all-cancers among the Iranian immigrants remain to be established. The ASR difference between the Iranian immigrants and the Iranian residents may be due to the differences between the registry systems, selected immigrant groups and environmental exposures.