Elsevier

European Journal of Cancer

Volume 46, Issue 3, February 2010, Pages 599-605
European Journal of Cancer

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

https://doi.org/10.1016/j.ejca.2009.10.009Get rights and content

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.

Introduction

Global cancer incidence varies extensively between developed and developing countries. However, the differences between incidence rates at site-specific cancers are usually much larger than those between overall rates. This is due to the low incidence rate for all cancers in developing countries, but very high risk for site-specific cancers such as liver, oesophageal, stomach and cervical cancers.1, 2 Studies of migrants may provide valuable insight into the aetiology of cancer. Classical cancer studies on immigrants to the USA and Australia showed that the incidence in common cancers adapts to the level of the new host country in one or two generations.3 These findings were fundamental to the understanding of the environmental aetiology of human cancer. Studies in Sweden have shown that the second generation immigrants, those born in Sweden, have already adopted the Swedish cancer incidence rates. The first two decades of life are important in setting the pattern for cancer development in subsequent life.4, 5 In all, Sweden is an excellent choice of country for an immigrant cancer study because of a uniform cancer registration, the health care system and the large number of immigrants, around 13% of the population, from practically all around the world.

Immigrant studies are most informative when cancer incidence data are available from both the source and host countries, a requirement that has been met by few previous studies on non-European populations. The Iranian national cancer registry programme has been developed during recent years and can be used to estimate the incidence in the source country. The number of Iranian immigrants in Sweden is 3.7% of all immigrants. In the present study, we focus on Iranian migrants to compare their cancer risks to the native Swedish population and to Iranian residents. The results of this study might be used to gain insight into the causes of cancers and the prevention of cancer.

Section snippets

Materials and methods

The Swedish Family-Cancer Database (FCD) was first assembled from the national databases in 1996 and since then it has been periodically updated.6 The FCD contains information pertaining to those born in Sweden since 1932 together with their biological parents’ data. Additionally, data on immigrants are also included. This database is the largest in the world on familial cancer and its updated version (2008, VIII),7 which has been supplied with longitudinal demographic and socio-economic data

Results

Out of 65,501 Iranian immigrants in the FCD, 62,471 lived in Sweden at the end of 2006. The fifth decade was the main age group (about 30% of the population); over 48% of the Iranian immigrants immigrated to Sweden between 1985 and 1990 (during the war between Iran and Iraq) with a median age at immigration of 26 (range = 0 to 86) years and a median length of stay of 16 (range = 1 to 58) years at the end of 2006.

The population pyramids by age and sex for the three populations are shown in Fig. 1.

Discussion

This study compared the incidence trends and risks between the three populations. Immigrants are always a selected population, and usually a healthy one.3 However, residing in Sweden for 16 years allows time for exposure to environmental risk factors prevailing in the country. Wide variations in the incidence of breast, colon and stomach cancers have been shown in Iran, with North Iran having much higher incidence rates for stomach and oesophageal cancers than other parts of Iran; inversely,

Conflict of interest statement

None declared.

Acknowledgements

This study was supported by the DKFZ guest scientist programme, the Swedish Council for Working Life and Social Research, the Swedish Cancer Society, and Deutsche Krebshilfe. The used database was created by linking registers maintained at Statistics Sweden and the Swedish Cancer Registry. The authors would like to thank Ms. Rashmi B. Prasad for helpful comments and critical reading of the manuscript.

References (35)

  • K. Hemminki et al.

    The Swedish family-cancer database 2009: prospects for histology-specific and immigrant studies

    Int J Cancer

    (2009)
  • K. Hemminki et al.

    The nation-wide Swedish family-cancer database – updated structure and familial rates

    Acta Oncol

    (2001)
  • S.M. Mousavi et al.

    Gastric cancer in Iran 1966–2006

    Asian Pac J Cancer Prev

    (2009)
  • F. Kamangar et al.

    Esophageal cancer in Northeastern Iran: a review

    Arch Iran Med

    (2007)
  • S.M. Mousavi et al.

    Breast cancer in Iran: an epidemiological review

    Breast J

    (2007)
  • The National Board of Health and Welfare. Cancer incidence in Sweden 2006. cited. Available from:...
  • Cited by (14)

    • Trends in mortality after cancer diagnosis: A nationwide cohort study over 45 years of follow-up in Sweden by country of birth

      2015, Cancer Epidemiology
      Citation Excerpt :

      A national cancer strategy for Sweden was established in 2009 aiming at improving survival and quality of life among cancer patients and reducing geographical differences [2]. Though several studies have recently investigated the issue of cancer and migration [7–15], the major focus has so far been placed on comparing incident data. We evaluated equality with respect to access to health care and treatment by measuring mortality rates by year of diagnosis, age at diagnosis, sex, and time since immigration into Sweden using several national demographic and health registers.

    • Risk of lung cancer by histology among immigrants to Sweden

      2012, Lung Cancer
      Citation Excerpt :

      The age-standardized incidence rates (ASR) (per 100,000) was calculated by diving the number of cases into person year at risk. The world population was used for standardization [20–23]. We selected the countries of origin where had at least 50 male lung cancer cases (Tables 1 and 2).

    View all citing articles on Scopus
    View full text