Survival of Cancer Patients Treated with Non-Fermented Mistletoe Extract: A Systematic Review and Meta-Analysis

Background: Mistletoe extracts (ME) are used in integrative cancer care to improve quality of life and to prolong survival. ME are available from different producers and differ in pharmaceutical processing, such as fermentation. In contrast to fermented ME, the impact of unfermented extracts on the survival of cancer patients has not yet been assessed in a meta-analysis. Methods: We searched the databases Embase, CENTRAL, Europe PMC, Clinicaltrials.gov, Opengrey and Google Scholar, and selected controlled studies on cancer patients treated with non-fermented ME. We included randomized controlled trials (RCTs) and non-randomized studies of intervention (NRSIs). The risk of bias was assessed with Cochrane's ROB2 and ROBINS-I; a meta-analysis was conducted. Results: Eleven RCTs and eight NRSIs met the inclusion criteria. The studies were heterogeneous and their ROB2 and ROBINS-I displayed a moderate and high risk of bias, respectively. For RCTs, the pooled effect estimate of non-fermented ME on survival was HR = 0.81 (95% CI 0.69-0.95, P = .01). Subgroup analyses as well as the NRSIs estimation support the robustness of the finding. When active comparators are added to the analysis, the effect estimates become non-significant. Conclusion: The results may indicate a positive impact of non-fermented ME on the overall survival of cancer patients. High quality RCTs are necessary to substantiate our results. Prospero Registration: CRD42021233177