The gap between rare and common cancers still exists: Results from a population-based study in the Netherlands

Introduction: Epidemiological discrepancies exist between rare and common cancers. The aim of this population-based study was to compare rare versus common adult solid cancers in the Netherlands, by providing incidence, prevalence and survival rates, evaluating trends in survival and comparing individual entities within domains and families. Methods: All adult patients with malignant solid cancers in the Netherlands between 1995 and 2019 were identified from the Netherlands Cancer Registry. Data on patient, tumour and treatment characteristics were collected, and relative survival and survival trends were analysed. Results: A total of 170,628 patients with rare adult solid cancers and 806,023 patients with common adult solid cancers were included. Rare cancers accounted for 18% of all cancer diagnoses (mean incidence), and 15% of the total ten-year cancer prevalence during 2010–2019. Overall 5-year survival was worse for rare cancers than for common cancers (52.0% versus 68.7%). Between 1995–1999 and 2015–2019, 5-year survival rates for rare cancers increased to a lesser extent (from 46.2% to 52.6%, i.e. 6.4%) than for common cancers (56.9%–70.1%, i.e. 13.2%), and for most rare cancer domains compared to common cancer domains. The majority of rare cancer entities did not show an improvement in 5-year survival. Differences for individual entities between domains and families were found. Conclusion: Differences in survival between rare and common cancers indicate major challenges for rare cancer care and emphasise that improvement is highly needed. Observed inequalities need to be overcome by investing in early diagnosis, novel therapies, scientific research and in establishing centres of expertise.