1. What is mistletoe?

   Mistletoe is a semiparasitic plant that grows on several types of trees, including apple, oak, maple, elm, pine, and birch. It has been used for centuries to treat medical conditions such as epilepsy, hypertension, headaches, menopausal symptoms, infertility, arthritis, and rheumatism. Mistletoe is used mainly in Europe and Asia, where products are made and sold under brand names including Iscador, Eurixor, Helixor, Isorel, Vysorel, and ABNOBAviscum. Mistletoe products are not sold to consumers in the United States.

   The chemical makeup of mistletoe products varies, depending on many factors, including:

   • The type of tree on which the mistletoe plant grows.
   • The time of year the plant is harvested.
   • The species of mistletoe.
   • Whether the extract is fermented or unfermented.
   • Whether the extract is prepared with homeopathic methods.
   • The company that makes the product.

   This summary discusses research done mainly with a mistletoe species known as Viscum album Loranthaceae.

   Mistletoe extracts are prepared as water-based solutions or solutions of water and alcohol. Mistletoe products may be named according to the type of tree on which the plant grows. For example, IscadorM is from apple trees, IscadorP comes from pine trees, IscadorQ is from oak trees, and IscadorU comes from elm trees.

2. What is the history of the discovery and use of mistletoe as a complementary or alternative treatment for cancer?

   Mistletoe was used by the Druids and the ancient Greeks, and appears in legend and folklore as a "cure -all." Interest in mistletoe as a possible treatment for cancer began in the 1920s.

   Extracts of mistletoe have been shown to kill cancer cells in the laboratory and to boost the immune system (the complex group of organs and cells that defends the body against infection or disease). For this reason, mistletoe has been classified as a type of biological response modifier (a substance that stimulates the body's response to infection and disease).

   Ingredients in mistletoe that have been studied for their usefulness in treating cancer include:

   • Alkaloids.
   • Viscotoxins.
   • Lectins.

   One of the 4 different lectins, known as ML I (or viscumin), may produce many of mistletoe's effects.

3. What is the theory behind the claim that mistletoe is useful in treating cancer?

   Mistletoe extract is studied as a possible anticancer agent because it has been shown to:

   • Boost the immune system.
   • Kill cancer cells in the laboratory.
   • Protect the DNA in white blood cells, including cells that have been exposed to DNA-damaging chemotherapy drugs.

   Refer to the PDQ health professional summary on Mistletoe Extracts for more information on theory.

4. How is mistletoe administered?

   Mistletoe extracts are usually given by injection into the muscle (intramuscular), beneath the skin (subcutaneous), or into a vein (intravenous or IV). In most reported studies, injections under the skin were given 2 to 3 times a week for various lengths of time.

5. Have any preclinical (laboratory or animal) studies been conducted using mistletoe?

   Laboratory and animal studies have been done with mistletoe, either alone or combined with other agents. Laboratory studies have suggested that mistletoe may support the immune system by increasing the number and activity of various types of white blood cells.

   Animal studies testing mistletoe's ability to stop cancer cell growth have had different results depending on the extract used, the dose tested, the way it was given, and the type of cancer studied. Results of a few animal studies have suggested that mistletoe may be useful in decreasing the side effects of standard anticancer therapy, such as chemotherapy and radiation therapy, and that it may protect the immune system from certain drugs.

6. Have any clinical trials (research studies with people) been conducted using mistletoe?

   Clinical trials using mistletoe to treat cancer have been done in Europe with unclear results. Most study results have been published in German. Although many of these trials have reported mistletoe to be effective, there are major weaknesses in almost all that raise doubts about their findings. Weaknesses have included small numbers of patients, incomplete patient data, lack of information about mistletoe dose, and problems with study design.

   Much research about using mistletoe to treat cancer has focused on its effects on the immune system. Although there is evidence that mistletoe can boost the immune system, there is no evidence that this enhanced immunity helps the body to fight cancer cells.

   The National Cancer Institute's PDQ clinical trials database contains protocol abstracts for clinical studies of mistletoe as a treatment for cancer.[1]

7. Have any side effects or risks been reported from mistletoe?

   Very few bad side effects have been reported from the use of mistletoe extract products. Common side effects include soreness and inflammation at injection sites, headache, fever, and chills. A few cases of severe allergic reactions, including anaphylactic shock, have been reported.

   Although mistletoe extracts appear to be safe, mistletoe plants and berries are toxic (poisonous) to humans. Side effects caused by eating mistletoe plants and berries include seizures, slowing of the heart rate, abnormal blood pressure, vomiting, and death. These toxic effects may be more or less severe depending on the amount and the type of mistletoe plant eaten.

8. Is mistletoe approved by the U. S. Food and Drug Administration (FDA) for use as a cancer treatment in the United States?

   The United States Food and Drug Administration (FDA) has not approved the use of mistletoe as a treatment for cancer or any other medical condition. The FDA does not allow injectable mistletoe extracts to be imported or used except for clinical research.

   At this time, there is not enough evidence to recommend the use of mistletoe as a treatment for cancer except in carefully designed clinical trials. These trials will give more information about whether mistletoe can be useful in treating certain types of cancer.

References

1. Mansky PJ, National Center for Complementary and Alternative Medicine: Phase I Study of Gemcitabine and Mistletoe in Patients With Advanced Solid Tumors, NCCAM-02-AT-260, Clinical trial, Closed.  [PDQ Clinical Trial]
   
   

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