The most effective conventional method of preventing tumor recurrence is adjuvant intravesical (instilled through a catheter directly into the bladder) immunotherapy with bacillus Calmette-Guerin (BCG). This live bacteria is known to produce side effects, such as fever, blood in the urine, nausea and vomiting, joint pain and coughing.
Although experts have cast about for side-effect-free immunoactive substance that is just as efficacious, they have yet to identify one.
For the phase I/II clinical study published in the Journal of Urology (174(1):76-79, July 2005), researchers intravesically administered an aqueous mistletoe extract standardized to mistletoe lectin to 30 patients with superficial urothelial bladder carcinoma.
Administration of the mistletoe began four weeks after the removal of tumors, and patients received 50ml of mistletoe extract once a week for six weeks. Mistletoe lectin concentrations were between 10 and 5,000 ng/ml and the extract was retained in the bladder for 2 hours.
The researchers report that none of the patients displayed local or systemic side effects, and within 12 months tumor recurrence was 33 percent - comparable to the recurrence rate in patients treated with BCG.
"From these results it is concluded that standardized mistletoe extract could be a potential alternative adjuvant therapy for superficial bladder cancer," wrote the researchers.
"Nevertheless, the optimal intravesical treatment regimen has yet to be defined."
But Edzard Ernst, Britain's only professor of complementary medicine, told NutraIngredients-USA.com that this study appears to have been uncontrolled.
"It doesn't allow any conclusion about efficacy as we do not know what would have happened if the patients had not received mistletoe. All this study does say is that it is worth conducting a controlled clinical study, preferably randomized," he said.
He added that in the past, where positive results for mistletoe have been produced by uncontrolled studies, they have not stood up in controlled clinical trials that are not prone to bias.
Speaking at the European Breast Cancer Conference last March, Professor Ernst said:
"If an effective CAM treatment or preventative measure emerged (say, a herbal medicine) it would instantly be taken up by mainstream oncology, as has happened with taxol, which comes from the yew tree. It follows, almost automatically, that all existing CAM 'cancer cures' are bogus," he said.
He listed mistletoe amongst the CAMs that are promoted for cancer prevention or cure but with sparse scientific data to support such claims.
"Examples of risk include the adverse effects of herbal remedies, contamination or adulteration of herbal remedies, their interaction with prescribed drugs, and patients choosing to use an ineffective CAM instead of life-saving conventional treatment."
In 2003 Ernst published a meta-analysis of trials investigating the use of mistletoe to treat cancer in the International Journal of Cancer in 2003 which concluded that none showed efficacy in terms of improving quality of life, survival or other outcome measures.
"Most of the studies had considerable weaknesses in terms of study design, reporting or both," he wrote.