Mistletoe plant itself is quite poisonous but the extracts have been used as an alternative cancer cure in Europe. They have been given by injections in order to boost the immune system into fighting tumors.

British doctors have reported a case of a 61-year-old woman who reported a tumor-like mass in her abdomen after undergoing breast cancer treatment. Previously she had suffered from lymphoma and admitted taking mistletoe injections for lymphoma treatment.
The mass turned out to be an inflammation caused by the mistletoe treatment. However, it was not reported if the woman suffered any further side effects.

National Institutes of Health (NIH) reported that some studies showed that mistletoe extracts had potential for being used as cancer treatment. When the HIH conducted its own study, it proved that the previous researches have been flawed and that mistletoe produces additional side effects like joint pain and kidney failure.

The doctors are suggesting mistletoe use should be avoided as anything other than a holiday decoration. More importantly, they are also advising that the patients need to be up front with their doctors about alternative medications that they're taking.