Iscador® is an alternative patent medicine cancer treatment that uses extracts of European mistletoe, Viscum album. It was invented by Rudolf Steiner as part of anthroposophy, though it's not clear on what basis he thought it would work.
Unsurprisingly, it does bugger-all to treat cancer. It kills cancer cells in vitro (which, in alternative medicine terms, is huge success), so is the subject of continuing research, but has shown no clinical effectiveness as a drug.
As a popular form of cancer woo, it is highly controlled in the US to keep the quacks out. You can only even import the mistletoe extracts into the US for approved research. It's apparently readily available in Eastern Europe, though.