Our study compared the rates of selected cancers among three populations: hosts (Swedes), immigrants, and residents (Turks, Chileans, and NAs). By applying a 95% CI for the ASRs, our study was able to find significant differences in the rates of cancer after migration. However, a small number of cases (specifically among NA immigrants), the short follow-up period, lack of information on the birth province of immigrants, and defining only two groups of NA immigrants in the FCD were some limitations of our study. Furthermore, the population-based cancer incidence data in Turkey, Chile, and NA countries were based on regional data and only covered less than 7% of the total population (Zanetti et al., 2010; Population Data, 2011). For example, the incidence rates for Turkey were obtained from Izmir and Antalya. Both of these areas are in West Turkey and their rates may not apply to all parts of Turkey.
Classical immigrant studies on cancers have shown that the rate of cancer among immigrants reaches the level of the host country within the first or the second generation (Parkin and Khlat, 1996). Unexpectedly, our data showed that Turkish immigrant men had a rate comparable to that of Antalya residents and a decreased rate compared with the residents in Izmir, whereas the Turkish immigrant women showed no differences in the rates of cancer compared with the residents in Antalya and Izmir. However, their cancer rates did not reach the level of Swedes during the period of study. Furthermore, we found a 30% decrease in the all-cancer rate among Chilean immigrants compared with the residents in Valdivia (Curado et al., 2007). Such a decrease in the cancer rate was reported among Chinese immigrant men in Canada compared with the residents of Shanghai (Luo et al., 2004). In general, NA residents have all-cancer rates ranging from one-third to half of those among Swedes (The National Board of Health and Welfare, 2009; Zanetti et al., 2010), whereas our data showed that the rates among NA immigrants were from half to two-thirds of those among the Swedes. This finding indicates an estimated increase of 30–50% in the cancer rate among NA immigrants compared with the NA residents. The analyses by cancer sites (Tables 2–5) show that the observed decreased all-cancer rates in Turkish (men) and Chilean immigrants were mostly attributable to the decreased rates of lung and stomach cancers, whereas the increased rate of NAs was mostly attributable to the increased rate in prostate cancer.
Previous studies have shown a decreased rate of stomach cancer after immigration, particularly among immigrants from high-risk countries. For example, Japanese immigrants to the USA and Chinese immigrants to Canada had up to 80% decrease in the rate of cancer compared with the residents in Japan and China (Kamineni et al., 1999; Luo et al., 2004). Furthermore, an ∼50% decrease in the rate was reported among Korean–Americans compared with the Korean residents (Lee et al., 2007). We also found an ∼50% decrease in the rate of stomach cancer among Chilean immigrants compared with the residents in Valdivia. In addition, the higher rate of stomach cancer among Chilean resident men and the lower rate among Turkish resident women compared with the Swedes remained unchanged after immigration. Hence, our result shows that the risk for stomach cancer may be modified after migration (Nilsson et al., 1993; Moradi et al., 1998; Kamineni et al., 1999; Suerbaum and Michetti, 2002; Ferlay et al., 2010; Mousavi et al., 2011d).
Studies on Korean immigrants to the USA and Iranian immigrants to Sweden showed an increased risk for colorectal cancer compared with that among the residents in Korea and Iran (Lee et al., 2007; Mousavi et al., 2010b). Our data also showed an increased rate of colon cancer among NA men compared with the residents in Algeria and Tunisia. These findings suggest a shift in the original lifestyle to a Westernized lifestyle. However, we found that the lower rates of colon cancer among Chilean men, rectal cancer among Turkish men, and colorectal cancer among Turkish women compared with the Swedes remained lower after immigration. This finding indicates that the preservation of original habits might be the main environmental exposure influencing the risk for colorectal cancer among these immigrants. Thus, immigrants might show different behaviors in lifestyle changes after migration, which depends on the age at immigration (Mousavi et al., 2011a).
Previous studies have found a decreased rate of 20–30% in lung cancer among male Chinese immigrants to Canada and among Japanese immigrants to the USA (Kamineni et al., 1999; Luo et al., 2004). We also found a 50% decreased rate of cancer among Turkish men compared with the residents in Izmir. In addition, our data showed that the higher lung cancer rate among Turkish resident men compared with the Swedes remained higher after migration. Although information on smoking was unavailable in our database, this observation may be indicative of a modification in the prevalence of smoking after migration (World Health Organization, 2002; Nierkens et al., 2006; Mousavi et al., 2011c). We also found that Turkish women had an increased rate of lung cancer compared with the residents in Antalya and Izmir. This finding might be because of a selection bias in the migrant population (Parkin and Khlat, 1996). However, integration within the culture of a host country and changes in smoking habits, for example Swedish women smoke as much as men, could partly account for the differences observed in the rates of lung cancer among Turkish immigrant women (World Health Organization, 2002; Delander et al., 2005; Blomstedt et al., 2007).
We found that the rate of prostate cancer among Turks and NAs was up to seven times greater than the rate for residents in Turkey and NA countries (Beiki et al., 2009). We have previously reported a rate ratio of 4.1 for prostate cancer among Iranian immigrants in Sweden compared with the Iranian residents (Mousavi et al., 2010b). In agreement with our findings, one study showed that the rate of prostate cancer among US Koreans was 3.5 times greater than that for the Korean residents (Lee et al., 2007). In contrast, another study reported that Asian Americans born outside the USA had a rate of prostate cancer similar to that in the population of their birthplace (Cook et al., 1999). We also found that the rate of prostate cancer in Chilean immigrants was not significantly different from that in the residents in Valdivia. Although we believe that immigrants may not be a representative sample of the total population of a country of origin, exposures to new environment and changes in lifestyles, more precisely food habits, may explain our observation (Kocturk-Runefors, 1990; Cook et al., 1999; Palloni and Morenoff, 2001; Boyle and Levin, 2008). Although there is controversy with regard to the prostate cancer screening program, the lack of this program in the countries of origin and improvement in diagnostic efforts using the prostate-specific antigen in Sweden since the late 1990s are probable reasons for these differences (Berglund et al., 2005; Kjellman et al., 2009).
We found an increased rate of breast cancer among NAs compared with Algerian and Tunisian residents, whereas Turks and Chileans showed no differences compared with the residents in Turkey and Valdivia. Previous studies have reported an increased rate of breast cancer among Iranian immigrants to Sweden and Korean immigrants to the USA compared with the residents in Iran and Korea (Lee et al., 2007; Mousavi et al., 2010b). Overall, all immigrants, except for Moroccans, had lower rates of breast cancer than the Swedes. Differences in population aging, reproductive factors, lifestyles, a positive family history, and diagnostic facilities could explain the differences observed in the rates of breast cancer among immigrants, hosts, and residents (Lagerlund et al., 2002; Andreeva et al., 2007; Hemminki et al., 2008; Hemminki et al., 2011a, 2011b, 2011c).
Our data showed that the higher rate of testicular cancer among Chilean residents compared with Swedes remained higher after migration. On the basis of our previous publication on first-generation and second-generation immigrants, early environmental exposures play a major role in the etiology of testicular cancer (Hemminki et al., 2010c). We also found that the lower rate of kidney cancer among Turkish residents compared with the Swedes remained lower after migration. However, further studies are required to define the role of a new environment in the etiology of this disease (Uitewaal et al., 2004; Boyle and Levin, 2008; Mousavi et al., 2010c).
We found an increased rate of nervous system tumors among NA men and Turkish women compared with the residents in their countries of origin. However, those immigrants showed no significant differences in the rate compared with Swedes. As in our previous report, the genetic background and/or childhood exposures may play a role in the etiology of this disease rather than exposures after migration (Mousavi et al., 2011b). We found no change in the rate of thyroid cancer and NHL after migration. We have reported previously that an iodine imbalance or childhood exposure to ionizing radiation may be associated with a high risk of thyroid cancer among Asian immigrants (Mousavi et al., 2010a). NHL shows a large international variation in the rates (Curado et al., 2007). For example, the variation in the rate of NHL was about three-fold among NA residents (Table 3). Although our knowledge of the potential risk factors for NHL is limited, current evidence points to immunological factors in childhood, which might remain unchanged after migration (Hemminki and Li, 2002; Boyle and Levin, 2008).
The change in the all-cancer rate after immigration is varied among different immigrant groups. The differences observed in all-cancer rates among immigrants were mostly attributable to decreased rates for stomach and lung cancers or an increased rate of prostate cancer after migration. We observed increased rates of colon, breast, and nervous system cancers after migration, whereas the rates of testicular, kidney, and thyroid cancers, and NHL, remained unchanged. The observed differences in the rates of colorectal, breast, testicular, kidney, nervous system, thyroid cancers, and NHL between immigrants and hosts may confirm the role of early childhood exposures or the preservation of original lifestyles in the etiology of these diseases.
This study was supported by Deutsche Krebshilfe, the Swedish Cancer Society, the Swedish Council for Working Life and Social Research, the Swedish Research Council, and EU FP7/2007–2013 grant 260715. The results of this project were presented at the EUNAM meeting in Ferrara, Italy, on 8 September 2011.
Conflicts of interest
There are no conflicts of interest.
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Keywords:© 2013 Lippincott Williams & Wilkins, Inc.
cancer; Chile; immigrants; incidence; North Africa; residents; Sweden; Turkey