Online peer support for breast cancer survivors: A decentralized multicenter non-blinded parallel-group pilot randomized controlled trial (HOPE-BC study).

1668 Background: Peer support effectiveness for breast cancer survivors has reportedly varied, and no study has examined patient–supporter matching. This decentralized, multicenter, non-blinded pilot randomized controlled trial aimed to assess online peer support effectiveness and explore factors for a matching algorithm. Methods: Breast cancer survivors within three years of completing initial treatment were recruited and provided electronic informed consent. Based on the sample size estimation, the target sample size was set at 50. Participants were randomly assigned either to the peer support group, which scheduled an online peer support session immediately after registration, or to the waitlist group, which scheduled their session two weeks later. Participants could choose their preferred time and date through a web-based scheduling system. Peer support sessions were conducted online by two trained peer supporters. The primary outcome was the UCLA Loneliness Scale score, assessed one week after the session in the peer support group and at the end of the 2-week waiting period in the waitlist group. Secondary outcomes included satisfaction with peer support and other psychosocial measures, all collected through an electronic patient-reported outcome system. Effect sizes for outcomes were calculated to inform sample size estimation for future trials. Analyses were performed to explore factors associated with satisfaction. The study protocol was registered in the UMIN Clinical Trials Registry (UMIN000056741). Results: From February to July 2025, 54 participants enrolled and 52 individuals completed the study (27 peer support group, 25 waitlist group). At the primary endpoint, the mean (standard deviation) UCLA Loneliness Scale scores were 38.4 (11.2) in the peer support group and 41.3 (13.3) in the waitlist group (Cohen’s d = 0.24; t-test, P = 0.40). The change from baseline corresponded to a Cohen’s d = 0.32. Among the secondary outcomes, the changes in Generalized Anxiety Disorder-7 scores differed between groups (mean difference MD = -1.3; 95% CI = -2.5 to -0.1), and the changes in Patient Health Questionnaire-9 scores tended to be greater in the peer support group (MD = -1.2; 95% CI = -2.5 to 0.1). The global health status on EORTC QLQ-C30 did not differ between groups (MD = 1.0; 95% CI = -6.6 to 8.7). The median (IQR) satisfaction score was 46 (41.5, 50) on a 50-point scale. A linear mixed-effects model indicated that sharing ≥1 topic and age proximity between the participant and peer supporter were significantly associated with higher satisfaction. Conclusions: Results demonstrate the feasibility of future decentralized randomized trials on online peer support and provide effect size estimates to guide sample size planning. Shared topics and age proximity between participants and peer supporters may be considered when scheduling sessions.