Psychological Inflexibility and Quality of Life in Breast Cancer

Background: Psychological inflexibility (PI) is a transdiagnostic risk factor for emotional distress and diminished quality of life (QoL), yet the indirect pathways linking PI to QoL through distress remain largely untested in breast cancer. Methods: This exploratory secondary analysis used a publicly available longitudinal dataset of 40 women with non-metastatic breast cancer assessed at baseline and 2-month follow-up. Bootstrapped mediation (5000 resamples, BCa CIs) tested whether depression, anxiety, and stress (DASS-21) statistically mediated the association between PI (AAQ-II) and QoL (WHOQOL-BREF) across 27 models. Hierarchical regressions, Kruskal–Wallis tests, and extended correlations supplemented the analysis. Results: At follow-up, all nine cross-sectional indirect effects were significant (all 95% BCa CIs excluding zero), with distress accounting for 33–51% of the total association between PI and QoL. The largest indirect effects were observed for depression on psychological QoL (indirect = −0.845, p < 0.001) and anxiety on physical QoL (indirect = −0.739, p < 0.001). No indirect effects were significant at baseline or for change scores (all p > 0.05). Concurrent PI independently predicted psychological QoL (ΔR² = 0.094, p = 0.002), general QoL (ΔR² = 0.084, p = 0.015), and anxiety (ΔR² = 0.122, p = 0.004) in hierarchical regressions. Anxiety severity was associated with impairment across all five QoL domains (all p_adj < 0.05). Conclusions: These preliminary findings suggest that emotional distress may partially account for the association between PI and QoL in breast cancer, consistent with predictions from the ACT model. However, the small sample size and cross-sectional nature of the indirect effects observed at follow-up preclude causal inference. Replication in adequately powered prospective designs is essential.