Biobanks and registers in epidemiologic research on cancer.

The Nordic countries have a long tradition of register-based epidemiologic studies. Numerous population-based specialized registers offer high-quality data from individuals, and the extensive use of register data further improves the quality of the registers. Unique personal identity codes given to every resident and used in all registers guarantee easy and accurate record linkage. A legislation that makes the use of the existing data possible for purposes that benefit both registered individuals and the society - instead of forcing researchers to use their energy in repeated questionnaire studies, disturbing individuals' privacy and leading to response and recall biases - is a prerequisite for effective epidemiologic research. Biobanks can be considered an additional type of registers. They may offer data from individuals that cannot be reliably collected via questionnaire surveys. In turn, other types of registers are crucial in biobank-based studies (1) in defining for how long the persons in biobank cohorts are at risk of getting the diseases, (2) to get information on cofactors that may modify the relative risk measured by the biomarkers, and (3) to get information on the long-term outcome events. This chapter describes the possibilities of register use mainly in Finland - a typical representative of the Nordic "paradise of register-based epidemiological research" - in research of cancer etiology. The ongoing Nordic research project Changing work life and cancer risk in the Nordic countries (NOCCA) will be described as an example of a massive register use, including both direct linkages on an individual level and indirect group level linkages.