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 until March 2022. Of 6555 papers screened, 108 studies were included with 17,195 participants. Five meta-analyses of 77 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 (rpooled = -0.24, -0.39, -0.48, respectively); whilst higher scores on inflexible processes (experiential avoidance, cognitive fusion) were associated with higher distress (rpooled = 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 self-as-context, values and committed action and conduct mediation analysis in controlled trials of ACT processes on distress in cancer.
Keywords: Cancer; acceptance and commitment therapy; distress; meta-analysis; oncology; self-compassion.