An anonymous reader quotes a report from NPR: Scientists have long hoped that stem cells might have the power to treat diseases. But it's always been clear that they could be dangerous too, especially if they're not used carefully. Now a pair of papers published Wednesday in the New England Journal of Medicine is underscoring both the promise and the peril of using stem cells for therapy. In one report, researchers document the cases of three elderly women who were blinded after getting stem cells derived from fat tissue at a for-profit clinic in Florida. The treatment was marketed as a treatment for macular degeneration, the most common cause of blindness among the elderly. Each woman got cells injected into both eyes. In a second report, a patient suffering from the same condition had a halt in the inexorable loss of vision patients usually experience, which may or may not have been related to the treatment. That patient got a different kind of stem cell derived from skin cells as part of a carefully designed Japanese study. The Japanese case marks the first time anyone has given induced pluripotent stem (iPS) cells to a patient to treat any condition. The report about the three women in their 70s and 80s who were blinded in Florida is renewing calls for the Food and Drug Administration to crack down on the hundreds of clinics that are selling unproven stem cell treatments for a wide variety of medical conditions, including arthritis, autism and stroke.