Cancer risk among Scandinavian immigrants in the US and Scandinavian residents compared with US whites, 1973-89.

Studies of migrants can generate hypotheses on the aetiology of cancer. Such studies are most informative when cancer incidence data are available both in the source and host country. We compared the incidence rate ratio of cancers (stomach, lung, female breast, colorectal and prostate) in Scandinavian immigrants to the US to US-born whites, using data from the SEER registry, 1973-89. Odds ratios (OR) for cancer sites in relation to birthplace were estimated using logistic regression. We also compared rate ratios (RR) for Scandinavian and US residents, using Poisson regression. Compared with US whites, most Scandinavian migrant groups had elevated OR for stomach cancer (1.58 to 3.92), and lower OR for lung cancer (0.38 to 0.88). Similarly, compared with US whites, residents of most Scandinavian countries had elevated RR for stomach cancer (1.47 to 3.33) and lower RR for lung cancer (0.27 to 0.97). Therefore, risk factors for lung and stomach cancers, such as smoking habits and Helicobacter pylori infection, respectively, may have been retained upon migration. Risks for breast, colorectal and prostate cancer among immigrants approached risks in the US (contrasting Scandinavian risks) suggesting assimilation of environmental and/or lifestyle factors.