Preparing UNCAN.eu, a European initiative to understand cancer Overall and despite important progress, understanding of cancer remains incomplete, for both common and rare cancers. This requires a new level of investment in innovative research, including high-potential/high-risk projects. Therefore, a Mission on Cancer proposes a Europe-wide platform, "UNCAN.eu", utilising existing, relevant research infrastructures and investing in the development of models and technologies interrogating the interactions of poorly understood cancers[[Both common and rare cancers, or cancer subtypes, at all stages of cancer, any age or part of society.]] and their host.A fully-fledged "UNCAN.eu" initiative will:Underpin all future Mission on Cancer priorities that require a better understanding of poorly understood cancers;Agree on a strategic research and innovation agenda between afore-mentioned relevant stakeholdersIntegrate innovative models and technologies with longitudinal patient data (e.g. medical images), samples and biomarkers to deliver concrete benefits for people at risk of cancer, living with and after cancer;Allow for data interoperability and re-utilisation, while guaranteeing full protection for the data subjects and applying FAIR data principles. A comprehensive understanding of the organizational, logistic, cultural and financial feasibility, utility and sustainability would be necessary before embarking on such an endeavour.This coordination and support action aims to develop the operational concept for such an initiative.The proposal should address:Integration with ESFRI European Research Infrastructures, European Reference Networks, as well as other international cancer-centred research and data initiatives (e.g. 1+Million Genomes[[https://ec.europa.eu/digital-single-market/en/european-1-million-genomes-initiative]], SPECTA[[https://www.eortc.org/specta/]], etc.), as well as data exchange with national cancer data ecosystems;Sustainable and interoperable data platforms facilitating data access in compliance with data protection legislation and ethical principles, which will be developed in the framework of a future Health Research and Innovation Cloud, a thematic cloud under the European Open Science Cloud (EOSC)[[https://ec.europa.eu/info/research-and-innovation/strategy/goals-research-and-innovation-policy/open-science/eosc_en]], which will also address the data requirements of the European Health Data Space (EHDS)[[https://ec.europa.eu/health/ehealth/dataspace_en]] and be interoperable with it;Integration with other platforms proposed under the Mission on Cancer and the Europe’s Beating Cancer Plan, such as a network of comprehensive cancer infrastructures and a virtual European cancer patient digital centre;Mechanisms for determining clinical priorities and development of new models and technologies to interrogate the interactions of cancers and their host;Mechanisms for regular training on operating the "UNCAN.eu" platform as well as data management to all data holders and users;Potential links with Horizon Europe health cluster partnerships, in particular: the Innovative Health Initiative; the partnership on Personalised Medicine; the Transformation of Health and Care Systems partnership as well as the partnership on Rare Diseases and the Partnership for the Assessment of Risk from Chemicals.Providing a mechanism for regular consultation with EU regions, Member States and Associated countries, who should be engaged from the early steps of development;Potential links with EU4Health actions relevant for cancer;Links to federated data spaces of genomic data and medical images under the Digital Europe programme;Equitable access. Broad representation, in particular of less-developed regions or regions from countries striving to boost their research and innovation potential, is highly encouraged;Engagement with citizen and patient advocacy organisations;Utility, feasibility, sustainability;Due consideration to newly EU-funded initiatives such as HealthyCloud, EOSC-Life and the EHDS Joint Action. Links with topic HORIZON-INFRA-EOSC-2021-01-07; objectives are encouraged as well as with topic HORIZON-INFRA-SERV-2021-01-02 objectives.