PURPOSE: Breast cancer survivors are more likely to report psychological distress and unmet need for support compared to healthy controls. Psychological mobile health interventions might be used in follow-up care of breast cancer patients to improve their mental health. METHODS: We searched MEDLINE, PsychINFO, Cochrane and PROSPERO for articles on controlled trials examining the effectiveness of psychological mobile health interventions compared to routine care regarding mental health outcomes of adult breast cancer survivors. This review followed the PRISMA statement and was registered on PROSPERO (CRD42022312972). Two researchers independently reviewed publications, extracted data and assessed risk of bias. RESULTS: After screening 204 abstracts published from 2005 to February 2023, eleven randomised trials involving 2249 patients with a mean age between 43.9 and 56.2 years met the inclusion criteria. All interventions used components of cognitive behavioural therapy. Most studies applied self-guided interventions. Five studies reported percentages of patients never started (range = 3-15%) or discontinued the intervention earlier (range = 3-36%). No long-term effect >
3 months post intervention was reported. Three of seven studies reported a significant short-term intervention effect for distress. Only one study each showed an effect for depression (1/5), anxiety (1/5), fear of recurrence (1/4) and self-efficacy (1/3) compared to a control group. CONCLUSIONS: A wide variance of interventions was used. Future studies should follow guidelines in developing and reporting their mobile interventions and conduct long-term follow-up to achieve reliable and comparable results. IMPLICATIONS FOR CANCER SURVIVORS: No clear effect of psychological mobile health interventions on patients' mental health could be shown. REGISTRATION: PROSPERO ID 312972.