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.

Anyone who could be put off a life-saving treatment should probably relax, at least for now. The procedure used by the Hospital de Egas Moniz in Lisbon was unorthodox and bypassed a process that would have grown specific cells in a lab before implantation. Instead, the clinic simply inserted parts of the nasal lining straight into the spine, which is most likely why the tumor was able to form. Despite this, a 2010 report on this same trial found that there may be benefits to the procedure, with some subjects actually seeing positive results. Either way, now that the problem has come to light, the University of Iowa's Brian J. Dlouhy, who removed the tumor, has suggested that all stem cell trial patients should be given much more attention after their surgery to ensure this is a one-off event.