Objectives of the research project

The first objective was to establish a complete, population-based series of children and adolescents in the Nordic countries (Denmark, Finland, Iceland, Norway and Sweden) in whom cancer was diagnosed during the period 1943 to 2008. The childhood cancer survivors were followed-up individually to the present in various health-related national registers in order to investigate a range of treatment-related late complications in both survivors themselves and in their offspring.

Large Cohort

As a result of this international collaboration, an extraordinarily large cohort of childhood cancer cases (n = 55 000) has been established, with a combined populationcomparison cohort (n = 275 000) taken at random from the general populations of the Nordic countries. Accurate follow-up of patients and population controls were achieved through the civil registration systems of the Nordic countries, and use of large-scale record linkage techniques with national outcome registers provided a broad range of information on subsequent disease, independently of the person’s status as a patient or a population control. The combined dataset constituted a new, comprehensive, powerful surveillance instrument for estimating relative and absolute risks for medically verified, chronic health conditions in childhood cancer survivors. This is especially important for survivors age ?40 years, for whom there is little information on non-malignant outcomes.

Late effects

The second objective was to set up a number of clinical case-cohort studies of childhood cancer patients and their offspring, in which cases were defined on the basis of selected serious outcomes. These studies were designed to investigate damaging late effects of specific treatment regimens in childhood. The purpose is to contribute to the identification and characterization of high-risk populations, as this information is critical for making evidence-based recommendations for long-term follow-up of survivors of childhood cancer. Thus, the case-cohort design was applied to the childhood cancer survivor cohort as a hypothesis-testing instrument. Some outcomes have been be selected a priori, but the screening phase in the first part of the study identified any important new questions to be investigated. Detailed information on childhood cancer treatment was obtained from the medical records of the patients and from other sources.