["Psycho-Oncology, Volume 35, Issue 6, June 2026. ", "\nABSTRACT\n\nObjective\nThis study investigates how adult only‐child patients with advanced cancer and their parental caregivers appraise and manage uncertainty throughout the disease trajectory and how this process influences family relationships.\n\n\nMethods\nA longitudinal qualitative study was conducted with 10 patient‐parent dyads (20 participants) in a tertiary hospital in southern China. Semi‐structured interviews were conducted at three time points. Data were analyzed using reflexive thematic analysis guided by uncertainty management theory.\n\n\nResults\nThree themes emerged. First, dyads practiced mutual concealment for protection, withholding negative information to shield each other, a strategy that evolved from complete secrecy to selective disclosure. Second, shifts in coping strategies occurred, where the focus transitioned from seeking medical certainty to accepting ambiguity. Patients actively mitigated anxiety about their parents' future through financial and care planning. Third, family relationships were characterized by coexisting conflict and adaptation, as coping rhythms moved from early friction toward coordination, while parent‐child boundaries gradually dissolved as physical dependence deepened.\n\n\nConclusion\nIn only‐child families, adult patients and aging parents co‐manage the uncertainty induced by illness through mutual protection and specific future planning. Although this coping style contributes to maintaining the stability of the family system, it also results in restricted emotional expression. Healthcare and social support systems should attend to the evolving needs of this dyad throughout the disease trajectory and provide psychosocial support and community caregiving resources that are aligned with each stage of the illness.\n\n"]