Comparable data on cancer incidence and mortality in Denmark, Finland, Iceland, Norway, and Sweden are available for analysis through a collaboration of the national Cancer Registries via the NORDCAN website (http://ancr.nu). In the continued spirit of Nordic collaborative research, a number of studies examining trends in cancer survival are published in this journal.
Material and methods: The data were divided into eight 5-year periods by sex in five Nordic countries. Age-standardised 5-year relative survival ratios and excess mortality rates in the short-term (first month and 1-3 months following diagnosis), and the long-term (2-5 years after diagnosis) were calculated, as were age-specific 5-year relative survival using cohort-survival methods. A hybrid method combining the cohort and period methods was used for the period 1999-2003 as not all patients were followed for five years. Age-standardisation used the International Cancer Survival Standard, and calculation of expected deaths used country-specific population mortality rates.
Results: The data series constitutes 3 360 397 tumours among 3 160 802 patients followed up for death through 2006 for 39 different cancer sites diagnosed in the years 1964-2003. The paper describes the data, exclusions and imputations, design and analysis, age structure and standardisation procedures, follow-up, and case-mix adjustment methods.
Conclusion: The strengths of this study include the overall comparability and quality of the data, the national coverage, and the length of the time series. Collecting and analysing data from the five Nordic countries for 39 different cancer sites over 40 years in a systematised and comparable way is a major undertaking. A thorough description of the analyses, definitions and exclusions in the survival study, supplemented with corresponding information on cancer incidence and mortality is needed for appropriate interpretation and comparison between countries, and between and within cancer sites. This information must be made available to provide appropriate interpretation of the site-specific results.