Objective: To examine the prevalence, risk factors and mechanisms of impaired health outcomes (short- and long-term medical and psychosocial effects and late effects) over time among a population-based sample of AYA cancer patients. Study design: Prospective, observational cohort study Study population: All AYAs diagnosed (18-39 years at primary diagnosis) with cancer (any type) within the first 3 months after diagnosis (eligibility window of 1 month to ensure all eligible AYA cancer patients can be included) in one of the participating centres (or treated in one of these centres) in The Netherlands. Main study parameters/endpoints: The main outcomes are medical (e.g. second tumour; survival; fertility) and psychosocial (e.g. distress) health outcomes. Other study parameters (covariates/moderators/mediators) are characteristics of the individual (e.g. age, sex, cultural background, partner status, educational level, occupation, tumour type, disease stage, body composition, comorbid conditions, coping style), characteristics of the environment (e.g. cancer treatment, lifestyle), and genetic and biological factors (e.g. family history of cancer, stress and inflammation markers (e.g. cortisol, IL-6), microbiome). Nature and extent of the burden and risks associated with participation, benefit and group relatedness: On an individual level, patients who participate are asked to complete questionnaires on an annual basis for at least 10 years. All sample collections will take place at three time points: 0-3 months after diagnosis (baseline), 2 and 5 years; except blood for DNA analyses which will only take place at baseline. The collection of blood, hair and faeces at three occasions is minimally invasive and the risks of blood draws, hair and fecal sampling are negligible. All safety measures and procedures will be performed according to local guidelines. Patients will not experience direct benefit from participation in the COMPRAYA study. By participating, patients will contribute to a better insight in the prevalence of impaired medical and psychosocial (age-specific) health outcomes in AYA and evidence on factors associated with these health outcomes. This will lead to better and more personalized cancer care and supportive care tools for future AYA cancer patients.