Most studies have been conducted in Europe, primarily in Germany and Austria. However, in 2002, the National Center for Complementary and Alternative Medicine in cooperation with the National Cancer Institute (NCI) began accruing patients to a phase I trial (NCCAM-02-AT-260) of mistletoe (Helixor A) and gemcitabine in patients with advanced solid tumors. The Helixor A and gemcitabine combination showed minimal toxicity with clinical benefit in 48% of patients.
Most of the recent randomized controlled clinical trials looked at outcomes such as survival, tumor response, tumor recurrence and quality of life. All of the outcomes showed a positive response to mistletoe therapy. A systematic review of all controlled clinical studies of mistletoe found consistent improvement in chemotherapy-associated fatigue as well as other quality-of-life measures.
A nonrandomized, case-control study of long-term mistletoe extract for patients with melanoma, showed a survival advantage among patients with high-risk disease.
A large cohort study on the effectiveness of Iscador as a treatment for people with rectal cancer, colon cancer, breast cancer, stomach cancer, or lung cancer, found that the treatment can produce a clinically significant increase in survival in cancer patients.
The use of Iscador as an adjuvant treatment has been examined in several studies involving many types of cancer, including stage I-III colorectal cancer, bladder cancer, and malignant melanoma. In these studies, Iscador proved safe and effective and also showed a significant survival advantage over untreated controls. [9,10,11,12]
In a three-arm (Helixor, chemotherapy or control) randomized trial of breast cancer patients, survival was equivalent between the group treated with Helixor and the group treated with chemotherapy, but the Helixor group reported better quality of life owing to fewer side effects of therapy. 
Another three-arm randomized trial of colorectal cancer patients reviewed the outcome of chemotherapy alone or with chemotherapy and Helixor in combination. The mean survival time of those treated with Helixor and chemotherapy in combination was almost twice that of patients treated with chemotherapy alone. 
There are numerous other studies have demonstrated a significant positive effect of Helixor or Iscador in various types of cancers, including breast, lung, lymphomas, ovarian, pancreatic and colorectal. [15, 16,17,18]
A study in 2006 looking at the outcome of long-term Iscador therapy in breast cancer patients in Germany, found the treatment had a clinically relevant effect on breast tumor progression as measured by overall survival as well as by the time to recurrences, lymphatic or distant metastases (spread). The study also found that, in the short term, there were distinct and significant psychological benefits noted in the women who used Iscador therapy in conjunction with their chemotherapy regimen, than with conventional therapy alone. 
To summarize, mistletoe lectin therapy has clinically and scientifically demonstrated to have the following health-promoting and anti-cancer actions:
- Inhibit metastasis and reduce tumor size
- Induces apoptosis (cancer cell death)
- Enhances the activity of immune cells (such as T-helper cells and natural killer cells), thereby engaging and supporting the body’s own immune system to target and destroy cancerous cells
- Improve survival for most types of cancer
- Improved quality of life in patients with cancer tumors including improved mood, sleep, endurance, appetite, chemotherapy tolerability and decreased fatigue and pain
- Counteracts some side-effects of chemotherapy and radiation
- Increases survival in some cancers when used in combination with chemotherapy
- Lowers the risk for cancer recurrence
Iscador is most commonly administered as a subcutaneous injection. Helixor is given either by injection or intravenously.
Mistletoe lectin therapy is best used in combination with other cancer therapies such as IV vitamin C, as well as other therapies that are often given in the form of oral supplementation. Recommendations are always made on an individual, case-by-case basis.