Mistletoe Therapy

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1. What Mistletoe Therapy Is

Mistletoe therapy uses aqueous extracts from the European mistletoe (Viscum album L.), a hemiparasitic shrub that grows on deciduous and coniferous trees. Application is usually subcutaneous, less frequently intravenous or intratumoral. Standardised preparations contain defined amounts of mistletoe lectins and viscotoxins, whose concentration varies according to the host tree (e.g. apple, pine, oak) and harvest time. The therapy forms part of anthroposophic medicine but is also used outside this context.

Essential for understanding the study situation is the diversity of the extracts: different manufacturing processes (e.g. fermentation, cold-water extract) lead to preparations with varying active-substance profiles. In addition, mistletoe preparations are often combined with other therapies, which makes isolating specific effects more difficult. The bioavailability of the active components is only partially clarified, and the dose-response relationship remains the subject of research.

2. What the Studies Show in Detail

The key human studies and the most important reviews — by indication, with population, duration, preparation, outcome measure and result as reported in the original works. Numbers appear only where the work states them.

Distribution of the controlled studies in humans by indication — the numbers are not additive, as one work may be assigned to several areas:

Oncology – Quality of Life

The studies covered various cancer entities and predominantly used established, validated questionnaires. Half of the studies combined VAE with chemotherapy, radiotherapy or surgery. Dosage and preparation of the VAE varied; subcutaneous injections in escalating doses (e.g. 0.01 mg to 10 mg three times weekly) were frequently used. 22 of the 26 RCTs showed a significant advantage for QoL, particularly in the domains of fatigue, sleep, exhaustion, nausea, appetite, depression, anxiety and general emotional as well as functional well-being. Three RCTs showed no differences; one study reported no results. All non-RCTs demonstrated a QoL advantage. Methodological weaknesses, such as lack of blinding or small sample sizes, were present in some studies; however, studies of higher quality also predominantly showed positive effects 1.

A randomised, open-label phase-III study from 2013 examined 220 patients with locally advanced or metastatic pancreatic carcinoma who received either VAE (subcutaneous injections in escalating dosage from 0.01 mg to 10 mg three times weekly) or no antineoplastic therapy. Median overall survival was 4.8 months in the VAE group versus 2.7 months in the control group (HR=0.49; p<0.0001). In the “good prognosis” subgroup, median survival was 6.6 versus 3.2 months (HR=0.43; p<0.0001); in the “poor prognosis” group it was 3.4 versus 2.0 months (HR=0.55; p=0.0031). The study was stratified by tumour stage, age and performance status. Limitations include the lack of blinding and the combination with supportive therapy in both groups 2.

A systematic review and meta-analysis from 2020 analysed 26 publications with 30 datasets on QoL in cancer patients undergoing mistletoe therapy. The pooled standardised mean difference for global QoL was d=0.61 (95% CI 0.41–0.81; p<0.00001) in favour of mistletoe therapy. Effects were stronger in younger patients, longer treatment duration and studies with lower risk of bias. 50% of the QoL subdomains (e.g. pain, nausea) showed significant improvements. However, most studies had a high risk of bias or methodological shortcomings, which limits the strength of the evidence. The meta-analysis included RCTs and non-RCTs with different cancer types and mistletoe preparations (e.g. Iscador, abnobaVISCUM) 7.

Hypothesis The consistent reports of improved quality of life in numerous studies suggest that mistletoe therapy may possibly play a supportive role in oncological treatment, particularly in alleviating therapy-related symptoms. However, uniform standards for dosage, mode of administration and concomitant therapies are lacking, which complicates direct comparisons. It is also unclear whether the effects are limited to specific cancer types or stages.

Oncology – Survival and Tumour Response

A randomised phase III study (EORTC 18871/DKG 80-1) from 2004 investigated 830 patients with high-risk melanoma (stage II: tumour thickness >3 mm; stage III: positive lymph nodes) after surgery. The patients were randomised to four arms: recombinant interferon-alpha2b, interferon-gamma, Iscador M (a mistletoe preparation) or no additional therapy. The median follow-up was 8.2 years. The hazard ratios (HR) for disease-free interval (DFI) were 1.04 (95% CI 0.84–1.30) for interferon-alpha2b vs. control, 0.96 (95% CI 0.77–1.20) for interferon-gamma vs. control and 1.32 (95% CI 0.93–1.87) for Iscador M vs. control. For overall survival (OS) no significant differences were found. The study found no benefit for Iscador M regarding DFI or OS, indicating a lack of efficacy in this population 3.

Nine RCTs and 13 observational studies examined survival: twelve studies (three of them RCTs) reported a statistically significant benefit, the remainder showed trends or no differences. Three RCTs and six observational studies assessed remission or time to recurrence: three studies (one RCT) found a significant benefit, the others showed mixed results or no differences. The methodological quality of the studies was heterogeneous, with many studies having small samples or lacking blinding. Mistletoe therapy was used in different dosages and preparations (e.g. subcutaneous injections), often alongside standard therapies 4.

A systematic review from 2009 identified 49 clinical studies on mistletoe therapy (Iscador) and survival in cancer patients. 41 studies provided sufficient data for a meta-analysis. The pooled HR for overall survival was 0.59 (95% CI 0.53–0.66; p<0.0001) in favour of mistletoe therapy. However, a clear publication bias (funnel-plot asymmetry) was evident, and randomised studies showed smaller effects than non-randomised studies (HR ratio: 1.24; 95% CI 0.79–1.92). The studies covered different cancer types and preparations, with dosage and duration of administration varying. The results suggest a possible survival benefit from mistletoe therapy, but are limited by methodological shortcomings and heterogeneity of the studies 5.

Hypothesis The data on survival and tumour response under mistletoe therapy show contradictory results. While some studies report benefits, methodologically robust studies show no significant effects. The heterogeneity of the studies (dosage, cancer type, concomitant therapies) makes a clear assessment difficult. Large, blinded RCTs with uniform endpoints and long-term follow-up are still outstanding.

Oncology – Specific Cancer Types and Supportive Effects

The median time to progression (TTP) was 4.8 months in the control group and 6 months in the Iscador group (p=NS). The median overall survival time was the same in both groups (11 months). However, chemotherapy dose reductions (13% vs. 44%; p=0.005), severe non-haematological toxicities (16% vs. 41%; p=0.043) and hospitalisations (24% vs. 54%; p=0.016) occurred less frequently in the Iscador group. The study found no significant effect on QoL or the total number of adverse events, but indicated a possible supportive effect of mistletoe therapy regarding the tolerability of chemotherapy in the investigated setting, without this being interpreted as clinical efficacy against the tumour 10.

An epidemiological cohort study from 2005 investigated 477 patients with resected squamous cell carcinoma of the head and neck region. The patients were randomised and received either adjuvant mistletoe therapy (ML-1-standardised preparation, subcutaneous injections) or no additional therapy. The study found no significant differences regarding disease-free survival (HR=0.959; 95% CI 0.725–1.268), 5-year survival rate, cellular immune response or QoL. Mistletoe therapy showed no efficacy in this population 6.

A randomised pilot study from 2012 investigated 32 patients with gastric carcinoma (stage Ib or II) after surgery who received either oral chemotherapy with doxifluridine or additionally mistletoe therapy (abnobaVISCUM® Quercus, subcutaneous injections three times weekly in escalating dosage). After 24 weeks the mistletoe group showed significantly better values for global health (p<0.01), increased leukocyte and eosinophil counts (p≤0.01) and a lower frequency of diarrhoea (7% vs. 50%; p=0.014). There were no significant effects on TNF-alpha, IL-2, CD16+/CD56+- or CD19+-lymphocytes. The study suggests a possible supportive effect of mistletoe therapy in gastric carcinoma, but is limited by the small sample size and lack of blinding 11.

Hypothesis Some of the controlled studies suggest supportive effects of mistletoe therapy, particularly in reducing chemotherapy-related toxicities and improving quality of life. However, the results vary according to cancer type, preparation and study design. Targeted studies on specific cancer entities with clearly defined endpoints and sufficient power are still outstanding.

Inflammatory Processes

The already mentioned randomised pilot study in 32 patients with gastric carcinoma (stage Ib or II) examined, in addition to quality of life, immunomodulatory effects of mistletoe therapy (abnobaVISCUM® Quercus, subcutaneous injections three times weekly in escalating dosage over 24 weeks). The study found no significant changes in cytokine levels (TNF-alpha, IL-2) or lymphocyte subpopulations (CD16+/CD56+, CD19+) compared with the control group. However, leukocyte and eosinophil counts rose significantly in the mistletoe group (p≤0.01). The study thus showed changes in individual blood values, but no significant changes in the investigated cytokine levels or lymphocyte subpopulations; a clinical immune effect was not investigated 11.

A systematic review from 2013 on interactions between herbal and synthetic medicinal products included Viscum album alongside many other plants. The review identified Viscum album as one of the plants with potentially severe immunomodulatory effects. The reported cases of inflammatory reactions with organ fibrosis or death are based on individual cases or small studies with low methodological quality. Most studies on mistletoe therapy show no severe immunosuppressive effects, but rather non-specific immunostimulatory or inflammation-modulating effects. Whether and under what conditions clinically relevant interactions with Viscum album occur is still to be clarified.

Hypothesis The immunomodulatory effects of mistletoe therapy are complex and appear to be dose- and context-dependent. While some controlled studies show mild immunostimulatory effects, there are indications of potentially harmful interactions, particularly in combination with other immunomodulatory therapies. Systematic investigations into the underlying mechanisms and the clinical relevance of these effects are still outstanding.

Safety and Tolerability

A systematic review from 2011 analysed studies that investigated higher dosages of Viscum album extracts (VAE >1 mg in humans, corresponding to >0.02 mg/kg in animals) or mistletoe lectins (ML >1 ng/kg). In total 69 clinical studies and 48 animal experiments were included. Dosages ranged up to 1500 mg VAE in humans and 1400 mg/kg in animals, as well as up to 6.4 μg/kg ML in humans and 500 μg/kg ML orally in animals. The most common adverse effects were dose-dependent flu-like symptoms, fever, local reactions at the injection site and mild non-specific complaints. One serious adverse event (anaphylactic reaction) was reported. Preclinical studies indicated non-specific immune stimulation without evidence of immunosuppressive effects. The clinical studies showed tolerability of mistletoe therapy, even at higher dosages, although the clinical relevance of the immunological effects in humans was not investigated 12.

However, severe non-haematological toxicities (41% vs. 16%; p=0.043) and hospitalisations (54% vs. 24%; p=0.016) occurred more frequently in the control group of this study. The results provide an indication that mistletoe therapy may be associated with better tolerability of chemotherapy, without itself causing severe adverse effects 10.

Hypothesis Mistletoe therapy appears to be generally well tolerated overall, with predominantly mild and transient adverse effects. Serious adverse events are rare, but can occur in individual cases. Systematic long-term studies on safety are still outstanding, particularly in combination with other oncological therapies.

Overall Picture

Mistletoe therapy is frequently used in complementary oncology, although the study situation is heterogeneous and in part contradictory. The most consistent results are seen in the improvement of quality-of-life parameters, particularly in the alleviation of fatigue, nausea, pain and emotional well-being. These effects were observed in some systematic reviews, albeit with methodological limitations such as lack of blinding, small samples or publication bias. The data on survival and tumour response are less clear: while some studies report benefits, methodologically robust studies show no significant effects. This applies in particular to randomised, blinded studies with clearly defined endpoints.

The safety of mistletoe therapy appears to be given overall, with predominantly mild and dose-dependent adverse effects such as flu-like symptoms or local reactions at the injection site. The immunomodulatory effects of mistletoe therapy are complex and not fully understood.

3. How Robust the Research Is

Research on mistletoe therapy focuses predominantly on oncology (a substantial proportion of the human studies). Further priorities are safety, immunomodulation and quality of life (several systematic reviews). Among the human studies mentioned, observational studies predominate, while controlled studies account for approximately one seventh of the total. The most frequently cited works are reviews or meta-analyses on quality of life, followed by individual studies on survival and preclinical immune parameters.

Methodologically, the field shows strengths and weaknesses: Controlled studies on quality of life are often randomised and blinded, whereas survival studies are frequently unblinded or conducted with small case numbers. The heterogeneity of the extracts and combination therapies hinder comparability. In addition, long-term data on safety and efficacy are often lacking. The most frequently cited reviews emphasise positive effects on quality of life, yet point to methodological limitations that restrict robust conclusions on clinical endpoints.

4. What Is Frequently Claimed — and What the Data Provide

5. The Most Robust Works

Ordered by strength of evidence, not by prominence. The complete evaluation comprises considerably more works; the most robust are listed here.

Controlled Human Studies

• 1 Review article: Influence of Viscum album L (European mistletoe) extracts on quality of life in cancer patients: a systematic review of controlled cli (2010)
• 2 Viscum album [L.] extract therapy in patients with locally advanced or metastatic pancreatic cancer: a randomised clinical trial on overall survival (2013)
• Mistletoe therapy in oncology (2008)
• 3 Final results of the EORTC 18871/DKG 80-1 randomised phase III trial. rIFN-alpha2b versus rIFN-gamma versus ISCADOR M versus observation after surgery (2004)
• 4 Viscum album L. extracts in breast and gynaecological cancers: a systematic review of clinical and preclinical research (2009)
• 5 Survival of cancer patients treated with mistletoe extract (Iscador): a systematic literature review (2009)
• 6 The effect of an adjuvant mistletoe treatment programme in resected head and neck cancer patients: a randomised controlled clinical trial (2001)
• 7 Quality of life in cancer patients treated with mistletoe: a systematic review and meta-analysis (2020)
• The Effect of Complementary and Alternative Medicine on the Quality of Life of Cancer Patients After Treatment: a Systematic Review and Meta-Analyses (2013)
• Mistletoe for cancer? A systematic review of randomised clinical trials (2003)
• 8 Mistletoe treatment for cancer review of controlled trials in humans (1994)
• A critical review of complementary therapies for cancer-related fatigue (2007)
• 9 Efficacy and safety of mistletoe preparations (Viscum album) for patients with cancer diseases. A systematic review (2009)
• 10 Mistletoe as complementary treatment in patients with advanced non-small-cell lung cancer treated with carboplatin-based combinations: a randomised ph (2013)
• 11 Quality of life, immunomodulation and safety of adjuvant mistletoe treatment in patients with gastric carcinoma - a randomized, controlled pilot study (2012)
• Mistletoe in oncological treatment: a systematic review : Part 1: survival and safety (2019)
• Safety and Efficacy of the Long-Term Adjuvant Treatment of Primary, Intermediate to High-Risk Malignant Melanoma (UICC/AJCC Stage II and III) with a s (2005)
• Phase II study of viscum fraxini-2 in patients with advanced hepatocellular carcinoma (2004)
• Mistletoe extracts standardised in terms of mistletoe lectins (ML I) in oncology: current state of clinical research (2002)
• Quality of life and neutropenia in patients with early stage breast cancer: a randomized pilot study comparing additional treatment with mistletoe ext (2009)
• The use of herbal medicine in cancer-related anorexia/ cachexia treatment around the world (2012)
• Correlation of immune cell activities and beta-endorphin release in breast carcinoma patients treated with galactose-specific lectin standardized mist (1998)
• Additional Therapy with a Mistletoe Product during Adjuvant Chemotherapy of Breast Cancer Patients Improves Quality of Life: An Open Randomized Clinic (2014)
• Prospective controlled cohort studies on long-term therapy of ovairian cancer patients with mistletoe (Viscum album L.) extracts iscador (2007)

6. Summary

Systematic reviews and meta-analyses indicate improvements in quality of life, particularly regarding therapy-related symptoms such as fatigue, nausea, pain and emotional well-being, albeit with methodological limitations such as lack of blinding or small sample sizes. Supportive effects, for example the reduction of chemotherapy toxicities, are likewise documented, albeit in smaller studies with heterogeneous designs. The safety of the therapy is considered good, with predominantly mild and transient side effects.

Hypothesis The consistent reports on quality of life suggest that mistletoe therapy could play a supportive role in oncological treatment, particularly for alleviating distressing symptoms. This could be attributable to the heterogeneity of the extracts, differing dosages or concomitant therapies. Hypothesis: The immunomodulatory effects of mistletoe therapy are dose- and context-dependent; mild immunostimulatory actions are plausible, whereas severe interactions (e.g. with immunotherapies) have been reported in individual cases but have not been systematically investigated. The supportive effect could arise from non-specific effects such as inflammation modulation or stress reduction, without direct antitumour mechanisms.

To define the role of mistletoe therapy in oncology more clearly, large, blinded RCTs with uniform endpoints would be required. These should encompass specific cancer entities, standardised extracts and dosages as well as long-term follow-up. Clarification is needed in particular regarding: (1) the dose-response relationship and bioavailability of the active components, (2) the efficacy in combination with modern immunotherapies (e.g. checkpoint inhibitors), (3) the immunological mechanisms and potential interactions, (4) the long-term safety with chronic use and (5) the cost-benefit ratio in comparison with established supportive therapies. In addition, future studies should clearly differentiate between specific cancer types and stages in order to enable targeted recommendations.

7. What Remains Open

• Standardisation: How do different extracts and manufacturing processes affect efficacy?
• Long-term effects: Are there robust data on safety and efficacy over several years?
• Mechanisms: Which immunological or cellular processes are responsible for the observed effects?