There is growing evidence that psychosocial interventions can have psychological benefits for people affected by cancer, including improved symptoms of mental health and wellbeing and optimised immune responses. However, despite growing numbers of music interventions, particularly singing, in cancer care, there is less research into their impact. We carried out a multicentre single-arm preliminary study to assess the impact of singing on mood, stress and immune response in three populations affected by cancer: carers (n = 72), bereaved carers (n = 66) and patients (n = 55). Participants were excluded if pregnant or if they were currently being treated with chemotherapy, radiotherapy or oral immunosuppressive drugs. Participants were regular participants in five choirs across South Wales and took part in one hour of group singing. Before and after singing, visual analogue mood scales, stress scales and saliva samples testing for cortisol, beta-endorphin, oxytocin and ten cytokines were taken. Across all five centres and in all four participant groups, singing was associated with significant reductions in negative affect and increases in positive affect (p < .01) alongside significant increases in cytokines including GM-CSF, IL17, IL2, IL4 and sIL-2rα (all p < .01). In addition, singing was associated with reductions in cortisol, beta-endorphin and oxytocin levels. This study provides preliminary evidence that singing improves mood state and modulates components of the immune system. Further work is needed to ascertain how this differs for more specific patient groups and whether repeat exposure could lead to meaningful, longitudinal effects.