Longitudinal Cohort Study of the Relationship Between Illness Perception, Perceived Social Support, and Psychosocial Quality of Life in Adolescents and Young Adults Newly Diagnosed with Cancer: Outcomes from a BRIGHTLIGHT Study

Background/objectives: Social support can enhance psychosocial health-related quality of life (PSQOL) in adult cancer patients. Adolescents and young adults (AYAs) with cancer face unique psychosocial challenges that intersect with key developmental milestones. Theoretical models propose that illness perceptions and social support are key determinants of coping strategies and long-term health outcomes in this context. These may be especially salient for AYAs, for whom peer relationships and identity formation are central. Methods: We explored how perceived social support and illness perceptions influence PSQOL over time in AYA cancer patients through a secondary analysis of the BRIGHTLIGHT longitudinal cohort study. Results: BRIGHTLIGHT followed 830 young people aged 13-24 across five time points (6-36 months post-diagnosis). Multi-level modelling revealed that PSQOL improved over time but remained consistently lower in females (mean: 69.62, 95% CI: 70.69 to -68.55). Greater perceived support from friends was associated with poorer PSQOL (beta: -0.77, 95% CI: -1.007 to -0.54) and linked to negative illness perceptions, longer hospital stays (beta: 0.01, 95% CI: 0.00 to -0.02), longer diagnostic intervals (beta: -0.009, 95% CI: -0.02 to -0.00), and poorer clinical communication (beta: 0.52, 95% CI: 0.01 to -1.03). A patient interpretation exercise with BRIGHTLIGHT's Young Advisory Panel contextualized these findings. Conclusions: While peer support could promote normalcy, it could also intensify distress through emotional pressure or social isolation. Future research should address not only access to social support but its quality and relevance to AYAs' unique psychosocial needs.