A randomized controlled trial on the effectiveness of a one-to-one peer support intervention on resilience, social support, and salivary cortisol in recently diagnosed women with breast cancer

•Breast cancer diagnosis can take a toll on patients' psychophysiological well-being. •Peer support may be one way to promote resilience and adaptation to the disease •Peer support increases resilience in breast cancer patients with chemotherapy •in the control group without chemotherapy, decreased levels of resiliency Purpose Peer support has been suggested as a way to help women diagnosed with breast cancer to better cope with their situation, but studies on its effectiveness have conflicting results. This randomized controlled trial aimed to study the effectiveness of a one-to-one peer support intervention on psychological resilience, social support, and salivary cortisol among breast cancer patients. Method The sample consisted of 121 newly diagnosed women at Onkologikoa Hospital. Patients who were prescribed chemotherapy were randomly assigned to Intervention Group 1 (IG1) or Control Group 1 (CG1). Similarly, those prescribed adjuvant radiotherapy were assigned to IG2 or CG2. Women in IG1 received 8 biweekly social support sessions from volunteer survivors who had successfully overcome breast cancer, while IG2 received 6 biweekly sessions. CG1 and CG2 only received standard care. Resilience, social support, and salivary cortisol were assessed at baseline (T1) and at the end of the intervention (T2). Results We found a non-significant, yet a small to moderate size increase in resilience from T1 to T2 in IG1 (p=0.246; dDc= 0.47). Upon regression analysis, we observed that this increase was determined by changes in cortisol (β = -.658, p= .010), affective support (β = -.997, p= .014), and emotional support (β = .935, p= .008). We also found a significant decrease in resilience levels in CG2 from T1 to T2 (p=0.003;dDc=0.88). Conclusion The present study suggests that peer support can exert a protective psychological influence on women diagnosed with breast cancer, and further indicates an exciting avenue for future intervention development in the breast cancer care continuum. Trial registration ClinicalTrials.gov NCT05077371. Peer support has been suggested as a way to help women diagnosed with breast cancer to better cope with their situation, but studies on its effectiveness have conflicting results. This randomized controlled trial aimed to study the effectiveness of a one-to-one peer support intervention on psychological resilience, social support, and salivary cortisol among breast cancer patients. The sample consisted of 121 newly diagnosed women at Onkologikoa Hospital. Patients who were prescribed chemotherapy were randomly assigned to Intervention Group 1 (IG1) or Control Group 1 (CG1). Similarly, those prescribed adjuvant radiotherapy were assigned to IG2 or CG2. Women in IG1 received 8 biweekly social support sessions from volunteer survivors who had successfully overcome breast cancer, while IG2 received 6 biweekly sessions. CG1 and CG2 only received standard care. Resilience, social support, and salivary cortisol were assessed at baseline (T1) and at the end of the intervention (T2). We found a non-significant, yet a small to moderate size increase in resilience from T1 to T2 in IG1 (p=0.246; dDc= 0.47). Upon regression analysis, we observed that this increase was determined by changes in cortisol (β = -.658, p= .010), affective support (β = -.997, p= .014), and emotional support (β = .935, p= .008). We also found a significant decrease in resilience levels in CG2 from T1 to T2 (p=0.003;dDc=0.88). The present study suggests that peer support can exert a protective psychological influence on women diagnosed with breast cancer, and further indicates an exciting avenue for future intervention development in the breast cancer care continuum.