RESUMO
BACKGROUND: Fear of progression (FOP) is a common and significant concern among cancer patients, encompassing worries about cancer progression during active treatment. Elevated levels of FOP can be dysfunctional. This study aims to assess the efficacy of an Acceptance and Commitment Therapy (ACT)-based intervention on FOP, anxiety sensitivity (AS), and quality of life (QOL) in breast cancer patients. METHODS: A clinical trial was conducted involving 80 stage I-III active-treatment breast cancer patients with a score greater than 34 on the Fear of Progression Questionnaire-Short Form scale. These patients were randomly assigned in a 1:1 ratio to either an intervention group, which received weekly 70-min sessions of 5-ACT-bsed group-therapy, or a control group that received usual treatment. Variables including FOP, AS, QOL, and ACT-related factors were assessed using ASQ, QLQ-C30, Cognitive Fusion Questionnaire, and Acceptance and Action Questionnaire-II at three time points: baseline, post-intervention, and 3-month follow-up. The efficacy of the intervention was evaluated using mixed model analysis across all time-points. RESULTS: The fidelity and acceptability of the ACT-based manual were confirmed using significant methods. A significant reduction in FOP was observed only in the ACT group at post-intervention (P-valueACT < 0.001; Cohen dACT = 1.099). Furthermore, the ACT group demonstrated a more significant reduction in FOP at follow-up. Furthermore, all secondary and ACT-related variables, except for the physical symptoms subscale, showed significant improvement in the ACT group compared to the control group. CONCLUSIONS: Our ACT-based manual showed promise for reducing FOP, AS, and improving QOL, and ACT-related variables in breast cancer patients 3 months following the intervention.