Mistletoe, a semiparasitic plant, holds interest as a potential anticancer agent because extracts derived from it have been shown to kill cancercellsin vitro[1,2,3,4,5,6,7,8] Reviewed in[9,10] and to stimulate immune system cells both in vitro and in vivo.[11,12,13,14,15,16,17,18,19] Reviewed in [10,20,21,22,23,24] Two components of mistletoe, namely viscotoxins and lectins, may be responsible for these effects.[25,26,27,28,29,30,31,11,12,13,17,18,19] Reviewed in [10,21,22,23,32] Viscotoxins are small proteins that exhibit cell-killing activity and possible immune-system-stimulating activity.[1,6,18,19] Reviewed in [33,34] Lectins are complex molecules made of both protein and carbohydrates that are capable of binding to the outside of cells (e.g., immune system cells) and inducing biochemical changes in them. Reviewed in [10,35,36,37,38] In view of mistletoe's ability to stimulate the immune system, it has been classified as a type of biological response modifier. Reviewed in  Biological response modifiers constitute a diverse group of biological molecules that have been used individually, or in combination with other agents, to treat cancer or to lessen the side effects of anticancer drugs. Mistletoe extracts have been demonstrated in preclinical settings to have other mechanisms of action, such as antiangiogenesis.
Preparations from mistletoe extracts are most frequently used in the treatment of cancer patients in German-speaking countries. Commercially available extracts are marketed under a variety of brand names, including Iscador, Eurixor, Helixor, Isorel, Iscucin, Plenosol, and Abnoba-viscum. Some extracts are marketed under more than one name. Iscador, Isorel, and Plenosol are also sold as Iscar, Vysorel, and Lektinol, respectively. All of these products are prepared from Viscum album (Loranthaceae) (Viscum album L. or European mistletoe). They are not sold as a drug in the United States.
The chronic myeloproliferative disorders consist of chronic myelogenous leukemia, polycythemia vera (p. vera), primary myelofibrosis, essential thrombocythemia, chronic neutrophilic leukemia, and chronic eosinophilic leukemia. All of these disorders involve dysregulation at the multipotent hematopoietic stem cell (CD34), with one or more of the following shared features:
Overproduction of one or several blood elements with dominance of a transformed clone.
Hypercellular marrow/marrow fibrosis...
In addition to European mistletoe, extracts from a type of Korean mistletoe (Viscum album var. coloratum [Kom.] Ohwi) have demonstrated in vitro and in vivo cytoxocity in laboratory studies.[41,42,43,44,45]
Mistletoe grows on several types of trees, and the chemical composition of extracts derived from it depends on the species of the host tree (e.g., apple, elm, oak, pine, poplar, and spruce), the time of year harvested, how the extracts are prepared, and the commercial producer.[46,47] Reviewed in [8,48,36,49]
Mistletoe extracts are prepared as aqueous solutions or solutions of water and alcohol, and they can be fermented or unfermented.[6,46] Reviewed in [4,20,47,50,51,52,53] Some extracts are prepared according to homeopathic principles, and others are not. Reviewed in [10,54] In addition, the commercial products can be subdivided according to the species of host tree. Iscador, a fermented aqueous extract of Viscum album L. that is prepared as a homeopathic drug, is marketed as IscadorM (from apple trees), IscadorP (from pine trees), IscadorQ (from oak trees), and IscadorU (from elm trees). Helixor, an unfermented aqueous extract of Viscum album L. that is standardized by its biological effect on human leukemia cells in vitro, is marketed as HelixorA (from spruce trees), HelixorM (from apple trees), and HelixorP (from pine trees). Reviewed in  Eurixor, an unfermented aqueous extract of Viscum album L. harvested from poplar trees, is reportedly standardized to contain a specific amount of one of mistletoe's lectins (i.e., the lectin ML-1; refer to the History section of this summary for more information). Reviewed in  Some proponents contend the choice of extract should depend on the type of tumor and the gender of the patient. Reviewed in [49,51,56]