BACKGROUND: A considerable number of cancer survivors face difficulties in returning to work (RTW). More insight is needed on how to support employees shortly after cancer treatment and help them make the transition back to work. OBJECTIVE: To gain an in-depth understanding of how and under what circumstances a Cancer & Work Support (CWS) program, which assists sick-listed employees with cancer in preparing their RTW, works. METHODS: A qualitative design was used, inspired by Grounded Theory and Realist Evaluation components. Semi-structured interviews were conducted with RTW professionals (N = 8) and employees with cancer (N = 14). Interview themes covered experiences with CWS, active elements, and impeding and facilitating factors. Interviews were transcribed and analyzed by multiple researchers for contextual factors, active mechanisms, and the outcomes experienced. RESULTS: Respondents experienced the support as human centered, identifying two characteristics: ‘Involvement’ (‘how’ the support was offered), and ‘Approach’ (‘what’ was offered). Four themes were perceived as important active elements: 1) open connection and communication, 2) recognition and attention, 3) guiding awareness and reflection, and 4) providing strategies for coping with the situation. Variation in the experiences and RTW outcomes, appeared to be related to the personal, medical and environmental context. CONCLUSION: Both professionals and employees really appreciated the CWS because it contributed to RTW after cancer. This research shows that not only ‘what’ RTW professionals do, but also ‘how’ they do it, is important for meaningful RTW support. A good relationship in an open and understanding atmosphere can contribute to the receptiveness (of employees) for cancer support.