Ostermann T, Raak C, Bussing A. Survival of cancer patients treated with mistletoe extract (Iscador): a systematic literature review. BMC Cancer. 2009;9(1):451.
Meta-analysis of 49 studies on the clinical effects of a mistletoe extract (viscum alba extract) sold as Iscador on survival of cancer patients. Outcome data were extracted and expressed as hazard ratios (HR) using standard formulas.
Fifty-two publications on the clinical effects of Iscador use and survival were found. Eight of these papers cited the same data and were excluded. Another 4 studies were excluded because they utilized 2 different mistletoe extracts, Helixor and Iscador. The oldest study was published in 1963 and the most recent 2008.
Overall 3,388 patents were treated with Iscador and 7,253 served as controls.
The medical use of mistletoe can be traced back to Druid ritual. Rudolf Steiner popularized the use of mistletoe preparations in his system of anthroposophical medicine. That this therapy was derived from such an esoteric source may be why research results have been inconsistent. The bias that researchers bring to their study of mistletoe may be difficult to overcome. Results may be swayed by patient belief, and non-randomized studies are inherently suspect.
This paper is the most comprehensive and yields the most positive meta-analysis to date. There have been similar attempts at pooling data over recent years in order to gain more insight into whether mistletoe offers benefit, but those studies have not yielded such encouraging results.
Results may be swayed by patient belief, and non-randomized studies are inherently suspect.
In 2003, Ernst, et al, attempted to review the randomized clinical trials but concluded that statistical pooling was not possible because the primary studies varied so much and instead simply wrote a narration of results. In their conclusion they stated, “None of the methodologically stronger trials exhibited efficacy in terms of quality of life, survival or other outcome measures. Rigorous trials of mistletoe extracts fail to demonstrate efficacy of this therapy.”1
Kienle and Kiene in a 2007 paper analyzed 16 randomized and 9 non-randomized controlled trials that investigated mistletoe treatment of malignant diseases and reported that “the best evidence for efficacy of mistletoe therapy exists for improvement of QoL [quality of life] and reduction of side effects of cytotoxic therapies (chemotherapy, radiation).”2
Horneber, et al, in a 2008 Cochrane Review that analyzed randomized controlled trials on various mistletoe preparations wrote: “The evidence … that the application of mistletoe extracts has impact on survival or leads to an improved ability to fight cancer or to withstand anticancer treatments is weak.”3
In a June 2009 review on mistletoe effect on breast and gynecological cancers, Kienle, et al, analyzed data from 19 randomized, 16 non-randomized controlled studies, and 11 single-arm cohort studies. Their analysis found “some positive effects in breast and gynaecological cancer.”4
In the current study, however, Ostermann, et al, reached this conclusion: “Pooled analysis of clinical studies suggests that adjuvant treatment of cancer patients with the mistletoe extract Iscador is associated with a better survival. Despite obvious limitations, and strong hints for a publication bias which limits the evidence found in this meta-analysis, one cannot ignore the fact that studies with positive effects of VA-E [viscum alba extract] on survival of cancer patients are accumulating.”
The positive conclusions in the most recent review by Ostermann, et al, will be widely quoted by those promoting use of Iscador and probably ignored by those less inclined to its use. Instead they will point to other reviews that were unable to show benefit, and there is no shortage of these.
To further illuminate the issue, the authors of the current study suggest, “Future studies evaluating the effects of Iscador should focus on a transparent design and description of endpoints in order to provide greater insight into a treatment often being depreciated as ineffective, but highly valued by cancer patients.”
In the meantime, it is encouraging to read that this often-debated therapy, which is in such high demand by patients, may actually be of benefit.
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