Evidence-based integrative medicine as exemplified by adjuvant mistletoe treatment

Background Mistletoe treatment has a long tradition, especially in the German-speaking world, and is one of the most frequently used complementary medical treatments in patients with cancer. The clinical evidence, however, stands in contrast to experimental anti-tumour effects (in vitro, in vivo). How efficacious is mistletoe treatment against solid tumours? Methods Potentially relevant clinical trials on mistletoe treatment in patients with solid tumours were located using electronic databases (e.g. Cochrane Library, MEDLINE) and defined search terms (e.g. mistletoe, Viscum). For a trial to be included in the analysis, mistletoe preparations had to be evaluated in a randomized, placebo-controlled manner, or within a comparative control study. The interventions had to be described in a clear and comprehensible fashion. For purposes of external validity, cohort studies were also considered. Results A total of 19 clinical studies satisfied the inclusion criteria and were evaluated. In terms of methodology, the internal validity of the controlled studies varied considerably and was usually low. The heterogeneity of the studies (e.g. different mistletoe preparations, interventions, tumour entities) made it impossible to conduct a meta-analysis. The results of the studies were inconsistent with regard to efficacy as measured in terms of survival times. Most of the studies, however, showed improved quality of life in patients on mistletoe treatment in addition to oncological therapy, thus underscoring the role of mistletoe as an adjuvant. In terms of safety, one serious adverse event was reported in association with mistletoe treatment. Frequent adverse events were local reactions (e.g. redness, induration); allergic reactions were rare. Conclusion Despite the methodological limitations of the included clinical trials, improved quality of life appears to be the most important measure of efficacy in adjuvant mistletoe treatment. The mistletoe preparations analysed in the studies showed good tolerability. Aspects related to quality of life are probably conditional on immunomodulatory (among other) effects. To date, however, clinical research has overlooked the potential of mistletoe treatment as a patient-oriented approach within a complex oncological setting. This should be investigated systematically in future studies, with an eye to quality of life.