ABSTRACT Context: In OECD countries with aging populations, more than one in eight people aged 50 and older have provided informal caregiving. In France, 10.5 million informal caregivers frequently and regularly provide unpaid care, on a non-professional basis, to individuals experiencing a loss of autonomy due to age, disability, or a debilitating chronic illness, helping them with all or part of their daily living activities. In oncology, advances in therapeutic approaches and patient management have often enabled outpatient and home-based care, putting a significant portion of the responsibility for monitoring, managing symptoms, and addressing treatment side effects on the patients themselves, as well as on their informal caregivers. Thus, even if the caregiving situation has positive effects (feeling of usefulness, strengthening of bonds, hope, reassurance etc.), it also has a substantial – sometimes detrimental - impact on the physical (unbalanced diet, increased consumption of alcohol, tobacco etc.) and mental (increased stress, sleep disorders etc.) health of the informal caregiver, especially if he/she is vulnerable. In this context, a pilot intervention providing support and prevention for informal caregivers of cancer patients was developed with informal cancer caregivers and evaluated from 2022 to 2024 at the Léon Bérard Cancer Center. Taking into account social determinants of health, the intervention consists of: 1) identifying informal caregivers, 2) raising their awareness, informing them, and supporting them in addressing mental and physical risks related to their role through two dedicated, personalized multidisciplinary prevention consultations, and 3) guiding, followingup and evaluating. The intervention, in its three steps, will also be developed as a digital tool. Objectives: To analyze the transferability of the intervention into two European institutions, ISPRO (Florence) and BIPS (Bremen), members of the Joint Action Prevent Non-Communicable Diseases. Methods: A comparative qualitative study of transferability based on the PIET-T process model and the ASTAIRE 2 tool will be conducted. Data will be collected through individual semistructured interviews, focus groups, observations and document analysis. Expected outcomes: Analysis of the characteristics of the target populations (P), of the compatibility of the intervention (I) in each target context, and of environments (E) will be conducted to compare differences and similarities, as well as barriers and facilitators with the primary context. Transfer (T) planning will also be carried out. This analysis will determine the transferability (T) of the intervention and thus inform the decision-making process regarding transfer, i.e., transfer without or with adaptations, or no transfer at all. Discussion-Conclusion: This international project will contribute to improving knowledge on the international transferability of support and prevention interventions to informal caregivers of cancer patients. The methodology developed and the results obtained can thus be used for other similar initiatives in Europe where these issues are public health priorities. The next steps, if the intervention is transferred, will be to implement the adapted intervention in both settings and evaluate its feasibility, acceptability, and outcomes on support, mental and physical health of informal cancer caregivers with a special focus on vulnerable ones.