The Inuit cancer pattern--the influence of migration

The Inuit cancer pattern is characterized by high frequencies of Epstein-Barr Virus (EBV)-associated carcinomas of the nasopharynx and salivary glands. The reasons are unknown, but genetic and environmental factors are believed to be involved. Using data from the well-defined Inuit population in Greenland we investigated whether migration to Denmark influenced their risk of cancer. Greenland is part of the Danish Kingdom, and population-based registries cover both countries. Using rates for Denmark as reference, sex-specific standardized incidence ratios (SIR) were calculated for Inuit who never lived in Denmark and for those who at least once were registered with a Danish address. During 1973-2003, we observed 3,567 cancers in a cohort of 77,888 persons. Of these, 862 among 26,214 Inuit ever living in Denmark, and 2,705 among 51,674 nonmigrating Inuit. High SIRs for cancers of the nasopharynx [31.7 (CI 22.0-45.5)] and salivary glands [3.1 (CI 1.4-6.9)] observed among Inuit migrating to Denmark were comparable to those observed among Inuit never living in Denmark. Significant higher risk of cancer of the bladder, breast, prostate gland, skin, brain and stomach was observed among Inuit following migration to Denmark. The SIR was not generally influenced by duration of stay. The high risk of carcinoma of the nasopharynx and salivary glands observed in Inuit populations is maintained after migration to a low incidence area. This indicates that genetic factors or environmental factors acting early in life are etiologically important for these cancers.