Journal of the National Cancer Institute Advance Access published online on December 25, 2007
JNCI Journal of the National Cancer Institute, doi:10.1093/jnci/djm276
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© The Author 2007. Published by Oxford University Press.
ARTICLES |
Testicular Cancer Risk in First- and Second-Generation Immigrants to Denmark
Affiliations of authors: Department of Epidemiology Research, Statens Serum Institut, Copenhagen, Denmark (CM, TW, TS, AO, JW, MM); Department of Natural Sciences, Copenhagen University, Copenhagen, Denmark (CR)
Correspondence to: Charlotte Myrup, MD, Department of Epidemiology Research, Statens Serum Institut, Artillerivej 5, 2300 Copenhagen South, Denmark (e-mail: cmy{at}ssi.dk).
Background: Immigrant studies offer insights into the relative importance of environment and genes in disease etiology. There is considerable variation in testicular cancer incidence worldwide. We investigated testicular cancer risk in first- and second-generation immigrants to Denmark, a high-incidence country, to evaluate the relative influence of genes and environment and the potential timing of action of environmental factor(s).
Methods: A cohort of 2.1 million men who were born since 1930 and lived in Denmark between 1968 and 2003 was established based on information in the Danish Civil Registration System, which included their immigration histories. Cancer histories were obtained from the Danish Cancer Registry. Testicular cancer risk was estimated as rate ratios (RRs) with 95% confidence intervals (CIs) based on log-linear Poisson regression.
Results: Overall, 4216 testicular cancer cases occurred during 43 million person-years of follow-up in 2.1 million men. These included 166 cases among 344444 direct immigrants to Denmark and 13 cases among 56189 men born in Denmark to immigrant parents. These first- and second-generation immigrants had RRs of testicular cancer of 0.37 (95% CI = 0.31 to 0.43) and 0.88 (95% CI = 0.51 to 1.53), respectively, compared with men born in Denmark of parents born in Denmark. The rate in first-generation immigrants was not modified by age at immigration or duration of stay and reflected that in the country of origin.
Conclusion: The testicular cancer risk in first-generation immigrants was lower than that in native-born Danes and reflected that in the countries of origin, whereas the risk in second-generation immigrants was similar to that in natives of Denmark. Together these findings argue for a substantial influence of environmental factors limited to the period early in life, most probably to the period in utero.
| CONTEXT AND CAVEATS Prior knowledge The incidence of testicular cancer varies worldwide and is especially high in Denmark. It has been unclear to what extent increased risk is due to environmental, rather than genetic, influences. Study design Testicular cancer risk in first- and second-generation immigrants to Denmark was analyzed using records obtained from the Danish Civil and Cancer Registries. Rate ratios were estimated by regression models. Contribution The risk of testicular cancer in men born in Denmark to immigrant parents was more than twice as high as the risk of testicular cancer among first-generation immigrants. Rates in first-generation immigrants were not associated with age at immigration or duration of stay in Denmark. Implications Environmental influences early in life, possibly prenatally, may contribute to testicular cancer risk. Limitations The number of second-generation immigrants analyzed was small.
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Manuscript received April 23, 2007; revised October 12, 2007; accepted November 16, 2007.
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J Natl Cancer Inst 2008 100: 1.