Rare cancers are generally classified in the group of rare diseases which is defined in the European Union as diseases with a prevalence of fewer than 5 cases out of a population of 10,000. A table published by the European Medicines Agency (EMA) with information on relevant sources for prevalence data for orphan conditions can be downloaded from the EMA Website.
Prevalence – the number of patients with the same diagnosis at a given time – is affected by mortality. However, it has been proposed by the Surveillance of Rare Cancers in Europe (RARECARE) project to consider a definition of rare cancers based on incidence, meaning the number of newly-diagnosed cases per year.
According to this definition, rare cancers are identified as those with an incidence of less than 6 per 100,000 persons per year. Using this definition would help minimise the risk of mistaking a rare cancer (such as testicular cancer), which is frequently cured and thus has a rather high prevalence, for a common cancer, or a frequent cancer (such as small-cell lung cancer), which has a low life expectancy and thus a low prevalence, for a rare cancer.
More information on the epidemiology of rare cancers is available here: www.rarecarenet.eu
See also the guidance for deliberations on rare cancer trial closures issued by the U.S. National Cancer Institute (NCI) Office of Cancer Centres on 22 May 2012.