Acceptance and commitment therapy processes and their association with distress in cancer: a systematic review and meta-analysis.

Around 42% of individuals with cancer experience distress. Acceptance and Commitment Therapy (ACT) can reduce distress, but effects are small, and mechanisms unclear. This review aimed to identify associations between ACT processes and distress in cancer. Search terms included cancer, ACT processes, self-compassion, and distress. Six online databases and grey literature were searched to March 2022. Of 6555 papers screened, 108 studies were included with a total of 17195 participants. Five meta-analyses of seventy-seven studies were conducted. Random effects meta-analyses of correlations revealed higher scores on flexible processes (acceptance, present moment awareness, self-compassion) were associated with lower distress ( = -0.24, -0.39, -0.48, respectively); whilst higher scores on inflexible processes (experiential avoidance, cognitive fusion) were associated with higher distress ( = 0.58, 0.57, respectively). Meta-analyses displayed moderate-to-high heterogeneity with most studies assessed as low risk of bias. Meta-regressions revealed no significant moderators (stage, time since diagnosis, gender and age). This review provides a theoretically aligned evidence base for associations between ACT processes and distress in cancer, supporting elements of ACT theory and providing targeted directions for intervention development. Due to limited evidence, future research should focus on the under-investigated processes (self-as-context, values, committed action) and conducting mediation analysis of ACT processes on distress in cancer in controlled trials.