PurposeIn hospital settings, patients, visitors, and staff engage in many interactions outside formal clinical encounters. Whilst many of these may be inconsequential, others contribute significantly to how patients and their carers experience cancer and its treatment. This article aims to explore the experiences and significance of interactions that occur outside formal clinical encounters in hospital cancer treatment settings.MethodsSemi-structured interviews were conducted with cancer patients, carers, and staff recruited from two hospital sites and cancer support groups. Hermeneutic phenomenology informed lines of questioning and data analysis.ResultsThirty-one people participated in the study: 18 cancer patients, four carers, and nine staff members. The experiences of informal interactions were grouped into three themes: connecting, making sense, and enacting care. The participants described how these encounters allowed connection with others in the hospital spaces, facilitating a sense of belonging, normality, and self-worth. Through these interactions, individuals participated in making sense of their experiences, to better anticipate the decisions and challenges that might lie ahead. By connecting with other individuals, they cared for others and felt cared for themselves, and were able to learn from, teach, and support each other.ConclusionsOutside the confines of the clinical discourses participants negotiate terms of engagement, sharing of information, expertise, and their own personal stories that they may employ to contribute to the individuals around them. These interactions occur within a loose and evolving framework of social interactions, an ‘informal community’, in which cancer patients, carers, and staff members play active and meaningful roles.Supplementary InformationThe online version contains supplementary material available at 10.1007/s00520-023-07900-6.