Edzard Ernst: Medicine man

Christmas - the time for mistletoe. Exotic rituals are associated with this legendary plant, including sacrificial ceremonies performed by ancient priests or druids. For a long time, mistletoe was associated with magical powers or considered sacred. Today's custom of kissing under it developed much later; originally it was believed to lead inevitably to marriage. Few know that mistletoe is also an alternative cancer treatment. Thousands of German cancer patients have injections of mistletoe extract as an adjunct to conventional cancer therapy and this is also being promoted in the UK.

Mistletoe cancer therapy goes back to Rudolph Steiner (1861-1925), the founder of anthroposophical medicine. Mistletoe is a parasitic plant - feeding off other plants - just as cancer is a parasitic tumour that lives off other tissues. Giving mistletoe extract to cancer patients might thus cure the disease, or at least ease its symptoms, Steiner thought. Far-fetched? Perhaps, but the followers of anthroposophy introduced the concept into medicine, and soon hundreds of cancer patients believed in it. Amazingly, test-tube studies even identified some anti-cancer activity in mistletoe extracts - but hundreds of plants have such properties and only very few are suited as cancer drugs.

When I first studied this therapeutic approach as a young clinician, I was told that it helped mainly by decreasing the suffering of cancer patients. Whenever I gave mistletoe injections, the results seemed encouraging. But young doctors are easily impressed, and I was no exception. What I didn't appreciate then was a relatively simple phenomenon: the hospital where I worked was well known for its approach across Germany; patients went there because they wanted this type of treatment. They were desperate and had very high expectations - and expectations can often move mountains, particularly in relation to subjective experience and symptoms. We call this "selection bias". It can give the impression that a therapy causes a positive health outcome even when it has no positive action of its own.

Years later I was again confronted with the mistletoe story - this time as a scientist. I wondered: are injections of mistletoe in any way superior to placebo injections? Looking for evidence, I found a large number of trials. But many were conducted along the lines of my earlier experience: patients who had heard about the benefits of mistletoe had chosen to receive this treatment. The outcomes were then compared with those of patients who had not wanted the therapy. In many instances the results implied positive effects of mistletoe. Some studies suggested that the symptoms of cancer were less severe when receiving mistletoe injections: others implied that mistletoe prolonged survival.

Only a few trials were designed rigorously to minimise bias. Their results showed that mistletoe offered no advantage over placebo - either in easing symptoms, or in survival, or in other cancer-related variables. When we evaluated all these studies, our conclusion was as disappointing as it was clear that "rigorous trials of mistletoe extracts fail to demonstrate efficacy of this therapy".

So what? Some people insist we should not discourage cancer patients from opting for mistletoe injections if they want them. This may reflect a humane attitude of wanting to help. Yet I fear it is not correct. Some studies suggest that serious harm might be caused by mistletoe injections. Rather than suppressing cancer, mistletoe might promote tumour cell growth in some malignancies.

Furthermore, about half of all patients suffer side-effects. And there is the "alternative" use of mistletoe to consider. Some patients are so convinced of its power that they abandon all other cancer treatments. They may even hasten their death. Responsible healthcare professionals should warn patients against using mistletoe as an alternative to conventional treatments.

Steiner's analogy was that mistletoe is a botanical parasite and thus it cures cancer, the parasite of humans. Perhaps Steiner should have focused on a less bizarre feature: cancer and mistletoe are both pests and threaten their hosts. The best way to control the pest is the radical removal of the parasite. Had he said this, Steiner would have become the champion of cancer surgery! The mind boggles.

Thanks to guardian.co.uk who have provided this article. View the original here.