Summary:
Viscum album extracts (VAE) are used in integrative cancer care to support immune function, reduce side effects, improve quality of life (QOL), and possibly improve survival and recurrence. The most common routes of administration are subcutaneous (SC) injection and intravenous (IV) infusion; most research pertains to SC administration. Proposed mechanisms of action include immunomodulation of both innate and adaptive immune response, and direct cytotoxicity. Increased lymphocytes (T cells, B cells, and NK cells), dendritic cells, cytokines including INF-gamma and IL6, and presence of IgG antibodies to mistletoe lectins and viscotoxins have been observed. SC and IV VAE are well tolerated; serious side effects such as allergy and anaphylaxis are rare but have been reported. Mild and self-limiting side effects including local injection site reactions (with SC use), fatigue, and mild fever are common. Studies in people with cancer have found that mistletoe is likely to support QOL, reduce symptom burden, and reduce side effects associated with treatment when given alongside standard care. Studies on survival and tumor response are not conclusive; some studies find benefit and others find no difference compared to control groups. VAE is not a cancer cure and not an alternative to conventional care. Overall methodological quality is poor, and studies with better methodology are less likely to find benefit to survival. In conclusion, mistletoe is a promising adjunctive therapy for QOL and side effect management, but more research is needed from well controlled studies to further elucidate its impact on survival and recurrence risk for people with cancer.