Mistletoe (Viscum album)

Pre-clinical studies

Misteltoe extracts have been shown, in various test models, to stimulate the immune system. 7-11 Animal studies have demonstrated that mistletoe extract increases DNA stability, 12 and inhibit cell growth. 13-14 Antitumour activity of Viscum album L. extracts has been reported from animal experiments. 10,15 It has also been suggested that mistletoe may be beneficial in decreasing the adverse effects of chemo- and radiotherapy and that it may counteract the effects of drugs used to suppress the immune system. 16-18

Uncontrolled trials

There are numerous uncontrolled clinical studies, which suggest anti-cancer effects of mistletoe. 19 Their results are open to bias and therefore less conclusive than those from controlled clinical trials. 20

Controlled trials and systematic reviews

Numerous reviews are available and their conclusions are somewhat contradictory. e.g.19,21-27 Observational and retrospective controlled clinical trials tend to generate encouraging results. e.g.22-23 A striking finding is the phenomenon that reports by investigators with affiliation to anthroposophical institutions invariably arrive at positive conclusions.

A Cochrane review (such assessments' tend to be scrupulously independent and transparent) aimed at determining the effectiveness, tolerability and safety of misteltoe extracts either as a monotherapy or administered as an adjunct to conventional cancer treatment. 24 The outcome measures considered included survival times, tumor response, quality of life (QoL), psychological distress, adverse effects of cancer therapies and safety of mistletoe extracts. Twenty-one randomised clinical trials (RCTs) met all the inclusion criteria. Thirteen of these studies investigated survival, and 6 of them showed some evidence of a benefit but none were of high methodological quality. Sixteen RCTs investigated QoL, psychological distress, performance index, symptom scales or adverse effects of chemotherapy. Fourteen of these studies showed some evidence of a benefit, but only two were of high methodological quality. The authors concluded that “the evidence from RCTs to support the view that the application of mistletoe extracts has impact on survival or leads to an improved ability to fight cancer or to withstand anticancer treatment is weak”. 24

A similar, but more recent systematic review, included 18 RCTs. 25 It confirmed the insufficient evidence in terms of life expectancy, but indicated positive effects on quality of life. The authors concluded, however, that the quality of the primary studies was "mostly low". Finally, these authors, were unable to identify marked differences between various preparations and advocate the use of the umbrella term "misteltoe therapy" for all of them.

More recently, Ostermann et al. evaluated 49 Iscador® studies with different designs. 26 They found relatively clear effects in favour of Iscador versus no treatment of survival. But there was evidence of publication bias and, focussing on just randomised studies, the effect was no longer significant.

Braedel-Ruoff specifically evaluated studies testing the effects of Iscador on natural killer cell activity. 27 She found that many of these trials demonstrated a positive effect. However, the evidence was not complelling and the author felt that more investigations were necessary to be sure.