A Dangerous Game: Some Athletes Risk Untested Stem Cell Treatments

In 2005, at the age of 32, then Los Angeles Angel Bartolo Colón won the American League Cy Young Award for best pitcher, one of professional baseball's top honors. He stumbled through subsequent seasons, however, after a series of rips and strains in the tendons and ligaments of his throwing arm, shoulder and back. In 2009 he all but quit baseball. Desperate to reclaim his career, Colón flew home to the Dominican Republic in 2010 for an experimental procedure not vetted or approved by the U.S. Food and Drug Administration. Doctors centrifuged samples of Colón's bone marrow and fat, skimmed off a slurry containing a particular kind of stem cell—immature, self-renewing cells that can turn into a variety of tissues—and injected it into his injured shoulder and elbow. Within months of the procedure the then 37-year-old Colón was once again pitching near the top of his game for the New York Yankees—commanding a 93-mile-per-hour fastball.

Whether the injected stem cells rejuvenated his arm is an open question. The fda and the International Society for Stem Cell Research warn that no...