Cancer risks in Nordic immigrants and their offspring in Sweden.

Numerous migrant studies on cancer have been carried out, but little data are available on cancer incidence upon inter-European migration. We used the nationwide Swedish Family-Cancer Database to analyse cancer risk among Nordic immigrants and their offspring in Sweden. The parental population had entered Sweden in their 20s and they had become parents in Sweden. Finns were the largest immigrant group including approximately 183,000 parents and 278,000 offspring. We calculated the standardised incidence ratios (SIRs) and 90 or 95% confidence intervals (CIs) for 26 cancer sites using native Swedes as a reference. Cancers in the first generation immigrants followed the rates in the countries of origin, reaching high SIRs for tobacco-related, cervical and testicular cancer among Danes and for stomach cancer among Finns. Only a few cancers, such as cervical cancer was increased in the second generation. At many sites, particularly among the Finns, protection was observed in the first generation. At three sites, breast, ovary and urinary bladder, where plausible evidence for protection was found even among offspring, this was not reinforced among the offspring of compatriot parents, which is inconsistent with heritable effects. Protection against melanoma was strongest among the offspring of compatriots, but the contribution of cultural factors cannot be excluded. As the parents immigrated to Sweden in their 20s, their cancer pattern, including habits and life style, appeared to be set before that age because the differences to Swedes persisted even in cancers that predominate in old age. Immigrant populations would appear to be attractive subjects to study etiological factors of cancer at sites where causes remain poorly understood, such as testicular cancer.