The Story Behind the Cancer Statistics

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The relationship between prevalence, incidence and mortality. The prevalence is the proportion of a population that has a certain cancer at a specific time point and depends on the incidence and mortality of the cancer.

Cancer rates are steadily increasing worldwide and are projected to continue to rise during the next decade. But what part of it is a true increase and what part is influenced by other factors, such as reporting and quality of various cancer registries, is unclear. In this week's blog post, we will highlight some of the common terms used when discussing cancer statistics and what to consider when interpreting it.

Cancer statistics provide an invaluable toolbox for researchers, not only in their aim to find risk factors, new treatments and diagnostic tools but also for healthcare planning and policies to reduce the cancer burden. That fact there is an increase of patients that develop cancer is well established, but it is important to consider all factors that are behind the data. Increased life expectancy has a large impact, but there are also several other environmental factors that need to be taken into account.

Incidence describes the number of newly diagnosed cases of cancer at a specific time point. The incidence is often given for the number of new tumors but can also be used to describe the number of patients that develop cancer at a specific time point. This means that the incidence of new tumors can be higher than the number of individuals since each individual can have more than one primary tumor. Incidence figures are often given as a fraction of a population, for example number of tumors per 100.000 individuals, to allow for easier comparison between different data sets. Social awareness, availability of screening programs and advances in detection techniques are other factors that affect the incidence of cancer. To control for differences in age distribution in different populations, incidence figures should be age-adjusted.

Prevalence, most often given as a fraction per 100.000 individuals, refers to the number of alive individuals who have been diagnosed with a certain cancer during a specific time period. Prevalence differs from incidence since it refers to both newly and previously diagnosed patients, and thus provides a measure also of patients that live long or have been cured from cancer.

Mortality, also most often given as fraction per 100.000 individuals, is defined by the number of deaths from a certain cancer during a certain time period. Some cancer types are diagnosed at a very late stage which will cause a higher mortality rate compared to cancer types that are discovered at an early stage.

Fluctuations in the rate of less common forms of cancer must be taken with caution, since a small change in the number of diagnosed cases can cause a relative large change in the statistics.

If you would like to learn more about cancer statistics, check out the latest data from the Globocan Cancer Observatory. In the Pathology Atlas, we explore proteins in different cancer types and how they are related to patient survival.

Charlotte Soläng