Evaluating the Effect of Acceptance and Commitment Therapy on Post-traumatic Growth in Cancer Survivors: A Pilot Non-randomized Controlled Trial in a Greek Sample

Background: Post-traumatic growth (PTG) is characterized by emotional, cognitive, and existential change and is associated with higher spiritual well-being and lower distress. Although Acceptance and Commitment Therapy (ACT) effectively reduces anxiety, depression, trauma symptoms, and fear of cancer recurrence in cancer survivors, PTG has rarely been examined in randomized or controlled trials. This pilot non-randomized controlled study evaluated an ACT-based intervention to promote PTG among Greek cancer survivors and explored its effects on psychological and physiological stress outcomes. Methodology: A pilot pre-post non-randomised controlled clinical trial design was conducted with 65 participants diagnosed with breast, colorectal, or head and neck cancer, recruited from two hospital oncology clinics. Participants were allocated to either an Intervention Group (IG), receiving a six-week ACT group program, or a Control Group (CG). Measures of PTG, anxiety, depression, traumatic stress, and salivary cortisol were collected at baseline (T1) and post-intervention (T2). Results: At baseline, groups were comparable across demographic and clinical variables. Following the intervention, the IG showed significant increases in overall PTG and in the Personal Strength factor. Anxiety and cortisol levels significantly decreased in the IG compared with the CG, whereas reductions in depression and traumatic stress did not reach significance after adjusting for baseline scores. Conclusion: Findings suggest that a brief ACT-based intervention can meaningfully enhance key dimensions of PTG and reduce anxiety among cancer survivors. As a pilot non-randomised controlled study, effect sizes and feasibility outcomes support the development of larger, fully powered trials incorporating long-term follow-up and biological stress markers.