Background: Many older patients with cancer have their family members, often their adult children, involved in a process of treatment decision making. Despite the growing awareness that family members can facilitate a process of shared decision making, strategies for involving family members are scarce. Furthermore, literature about shared decision making pays little attention on family relations or to the impact that these relations have on the decision process. The purpose of this study was to explore how surgeons and nurses perceive the involvement of adult children of older patients with cancer in treatment decision-making. Subsequently, it identified strategies to ensure family involvement in the decision-making process, used in clinical practice.

Methods: Semi-structured interviews were conducted with 13 surgeons and 13 nurses working in an university or general hospital. Qualitative content analysis was conducted according to the steps of thematic analysis.

Results: Both nurses and surgeons indicated that adult children's involvement in decision-making about treatment increases when patients become frail. They mentioned several characteristics of adult children's behaviour during the decision-making process. Most of these characteristics are beneficial, but they also can be challenging. The distinct nature of adult children's involvement can help older patients with cancer reach better-informed treatment decisions. Health professionals reported six strategies to support positive family involvement in decision-making about treatment.

Conclusion: Adult children may facilitate a process of shared decision-making and help patients reach well-informed treatment decisions. Health professionals' strategies deliberately support positive family involvement.