Stem cells are seen as one of modern medicine's most promising magic bullets, but that doesn't mean that we understand them. A paralyzed woman from the US has learned this the hard way, after an experimental treatment caused her to grow a nose-like tumor on her back. The unnamed person took part in a trial whereby stem cells from her nose were applied to her spine in the hope that it could repair the nerve damage that led to her paralysis. Unfortunately, the treatment was unsuccessful and, eight years later, the subject found worsening pain in that same area. When surgeons operated, they found a tumor comprised of nasal tissue that was producing a thick substance that was remarkably close to mucus.