Mediators of a Mindfulness-Based Intervention for Younger Breast Cancer Survivors: Effects on Depressive Symptoms

Objective Depression is associated with poor outcomes in breast cancer patients, with higher prevalence among younger women. Although mindfulness-based interventions (MBIs) have demonstrated therapeutic effects, the mechanisms of intervention effects are poorly understood. We investigated whether rumination, self-kindness, intrusive thoughts about cancer, cancer-related worry, or a sense of meaning and peace mediated the intervention effects of an MBI, Mindful Awareness Practices (MAPs), on depressive symptoms. Additionally, we explored the same variables as mediators of a psychoeducation program, Survivorship Education (SE). Methods Women diagnosed with stage 0–III breast cancer at age <50 years were randomized to 6 weeks of MAPs ( n = 85), SE ( n = 81), or wait-list control (WLC; n = 81). During preintervention, postintervention, and 6-month follow-up (FU), we assessed depressive symptoms, rumination, self-kindness, intrusive thoughts, worry, and meaning and peace. Results MAPs and SE significantly reduced depressive symptoms at postintervention, and reductions remained through 6-month FU for MAPs. Models revealed that reductions in rumination ( β = −0.68, 95% confidence interval [CI] = −1.64 to −0.07) and intrusive thoughts ( β = 1.17, 95% CI = −2.17 to −0.37) and improvements in self-kindness ( β = −1.09, 95% CI = −2.37 to −0.28) and meaning and peace ( β = −1.09, 95% CI = −3.16 to −0.56) mediated MAPs’ effects at all time points. Reductions in worry ( β = −1.34, 95% CI = −2.47 to −0.45]) mediated effects at postintervention only. Worry and intrusive thoughts mediated SE effects at postintervention and 6-month FU, respectively. Conclusions Findings identified depression-relevant mediators of MAPs’ effects, expanding the understanding of MBI mechanisms. Results highlight pathways that could be leveraged to optimize intervention outcomes. Trial Registration ClinicalTrials.gov identifier: NCT03025139.