Modern interest in mistletoe as a possible treatment for cancer began in the 1920s. For centuries, it had been used as something of a cure-all, but when mistletoe's immunostimulant properties were confirmed, the Druids' reverence for the healing power of this parasite got some scientific validation. Since then, lots of studies have been done in Germany, where many cancer patients augment conventional treatment with mistletoe extracts. In the lab, it kills certain cancer cells, while boosting the number and activity of white blood cells.
In 2002, the National Center for Complementary and Alternative Medicine in the U.S. began a Phase I clinical trial for a combination of mistletoe extract and cancer drugs in patients with advanced solid tumors. The data are still being analyzed but almost half the patients showed treatment benefit, and the mistletoe exhibited low toxicity. For now, the FDA doesn't allow injectable mistletoe to be imported or used in the U.S...except for clinical research.