Stage-Sensitive Effects of Mindfulness in Women with Nonmetastatic Breast Cancer: A Moderated Mediation Model of Body-Related Self-Conscious Emotions, Body Image Inflexibility, and Health-Related Quality of Life

Background This study investigated the mediating role of mindfulness in the relationship between body- and appearance-related self-conscious emotions (BASES) and two psychosocial outcomes—body image inflexibility (BII) and health-related quality of life (HRQoL)—in women diagnosed with nonmetastatic breast cancer. The moderating effect of cancer stage was also examined. Methods A cross-sectional sample of 302 women diagnosed with Stage 1 or Stage 2 breast cancer completed validated self-report measures, namely, the FMI-SF, BIPIS, and FACT-B. Partial least squares structural equation modeling (PLS-SEM) was employed to analyze direct and indirect relationships. Multigroup analysis (MGA) and MICOM procedures were utilized to evaluate moderation by cancer stage. The strength of mediation was assessed by bootstrapping (5,000 samples) and variance accounted for (VAF) indices. Results Mindfulness fully mediated the relationship between the BASES score and BII in Stage 1 patients (VAF = 89.4%); however, it only partially mediated this relationship in Stage 2 patients (VAF = 42.5%). With respect to HRQoL, mindfulness acted as a partial mediator in both stages, with consistently negative indirect effects (Stage 1 β = -0.283; Stage 2 β = -0.276). Moderation analysis revealed significant stage-specific differences in the strength of the mediation pathways, with patients in earlier stages demonstrating greater psychological flexibility and responsiveness to mindfulness. Conclusions Mindfulness emerges as a crucial protective factor against appearance-related emotional distress in early-stage breast cancer; however, its integration with other therapeutic approaches may be necessary in later stages. These findings advocate for stage-sensitive psychosocial interventions that address body image concerns and enhance quality of life in breast cancer care.