Résumé : Transdisciplinary (TD) research is increasingly recognized as essential for addressing complex challenges in healthcare and research. Similarly, in recent decades, patient participation in health research has grown, and patients’ experiential knowledge helps shed light on their perspectives and preferences. In the context of cancer, challenges they face extend beyond pathology and treatment to encompass physical, psychological, social, and spiritual needs. We set out to take the very first step in our TD exploration together with patients as co-researchers in the Belgian TD project, “Symphony of Us” (aimed at better understanding and implementing the concept of “Patient Value” in oncology research). In this perspective paper, we reflect on building the team of co-researchers (academic scientists and patient-researchers), with a focus on the onboarding of the patient-researchers. We share our experience of the two key onboarding moments – a dedicated workshop and training – and outline the most important lessons learned and the challenges faced during this process, with emphasis on the gaps and research needs for research teams, funders, and universities. TD research offers new perspectives by combining expert and experiential knowledge, which requires specific modes of organization. Co-research can present many challenges and require a constant questioning of one’s practices and personal posture. There are practical, ethical, and emotional issues involved in patient participation. It is therefore necessary to build a solid, committed, and mutually trusting team by promoting a reflexive capacity that enables adjustment of the scientific approach and project design. We believe our trajectory could inspire and help other transdisciplinary teams aiming to collaborate with patients in meaningful ways, as well as universities and funders who wish to support similar collaborations.