Cancer patients often experience psychological distress as a result of their disease (Carlson et al., 2018). One approach to managing this distress is Acceptance and Commitment Therapy (ACT; Sauer et al., 2024; Sauer & Weißflog, 2025; Sauer et al., 2023). At the same time, inpatient hospital stays are becoming increasingly shorter, which is why there is a need for brief psychological interventions in the inpatient setting. Louise Zinndorf’s research project aims to develop and evaluate an ACT-based brief intervention for the inpatient psycho-oncology consultation service. Cancer patients are already screened using the NCCN Distress Screening (Mehnert et al., 2006). If their distress score is ≥ 5, they are informed about the study. After obtaining informed consent, participants undergo the baseline assessment and are assigned either to the intervention group (ACT-based brief intervention) or the control group (supportive psychoeducational brief intervention). A follow-up assessment 3–5 days after the intervention and a follow-up examination three months later complete the study design. The parameters examined include psychological distress, (prognostic) anxiety, depression, psychological flexibility, health-related quality of life, fatigue, sleep, cortisol levels, and the use of additional psycho-oncological counseling.