Accurate international comparisons of cancer incidence and mortality can not only be tricky but can sometimes be impossible with the quality and quantity of cancer data often varying considerably from country to country.
Canada is among the few countries that maintains a population-based registry that records virtually all cases of cancer. Most countries maintain registries that cover selected cities and regions thought to be representative of the entire population. Still others collect data only from specific geographic areas and/or subpopulations. The registration of cancer cases and collection of data can be mandatory or voluntary. Moreover, cancer registries often compete for funding with other health care priorities.
In some countries, particularly in the developing world, cancers may be misdiagnosed or demographic and treatment data may be incomplete or inaccurate. On the other hand, in some countries such as the United States, there may be different sources of data and sometimes data collected from the same source is combined or adjusted in ways that create "new" databases.
According to Barbara Whylie, M.B., director of medical affairs and cancer control for the Canadian Cancer Society and the National Cancer Institute of Canada, Toronto, there are four key questions that should be considered when comparing international data: Are "true" differences being revealed? Do the differences reflect incomplete data? Are differences attributable to variations in accurate diagnoses? Are differences due not to additional cases but rather increased screening?
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Finally, some databases are better equipped to answer certain questions than others. It is important to know which databases can offer the best available information in terms of quality and quantity, Whylie said, adding that the sheer number of different resources can be daunting.
In Canada, cancer case data are collected from clinicians at the provincial level and reported to federal authorities who then make the data available through two federal agencies, Health Canada and Statistics Canada. Meanwhile, the best known U.S. database is the National Cancer Institutes Surveillance, Epidemiology, and End Results program, which collects cancer incidence and survival data from 11 population-based registries and three supplemental registries that represent approximately 14% of the U.S. population.
U.S. cancer mortality data are collected by the National Vital Statistics System of the National Center for Health Statistics. Other sources of primary or secondary data include the American College of Surgeons National Cancer Database; the American Cancer Societys Cancer Statistics Review, which reports SEER incidence data along with NCHS mortality data and also calculates projections; the North American Association of Central Cancer Registries, which is affiliated with the Centers for Disease Control and Preventions National Program of Cancer Registries and covers 44 U.S. states and the District of Columbia as well as Canada; and the CDCs Behavioral Risk Factor Surveillance System, which makes cancer screening and prevalence data available. In addition, national surveys such as the NCHSs National Health Interview Survey and the National Health and Nutrition Examination Survey can provide cancer-related data.
The best known sources of international data and research include the International Agency for Research on Cancer, Lyon, France, the International Union Against Cancer, Geneva, and the European Organization for Research and Treatment of Cancer, Brussels.
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