A new report suggests more clinics in the United States are offering potentially ineffective or harmful stem cell “treatments” without regulation from the Food and Drug Administration (FDA).

Researchers at the University of California and the University of Minnesota identified 351 U.S. companies marketing unapproved stem cell procedures at 570 individual clinics. Procedures include interventions for orthopedic injuries, neurological disorders, cardiac diseases, immunological conditions, pulmonary disorders, injured spinal cords, and cosmetic indications, according to a news release on the findings, which were published Thursday in the journal Cell Stem Cell.

The study authors, bioethicist Leigh Turner and stem cell researcher Paul Knoepfler, wrote in their report that it was unclear whether federal authorities, like the FDA, and state medical boards have underestimated the scope of the issue or whether they are taking minimal action despite their awareness.

"From around 2009 to the present, businesses have been entering the marketplace on a routine basis, they've been coming in making marketing assertions about stem cells treating 30-40 different diseases, and no one's taking meaningful regulatory action," study author LeighTurner, an associate professor in the Center for Bioethics at the University of Minnesota, said in the release. "Does that mean that people are getting access to safe and efficacious interventions or is there basically unapproved human experimentation taking place where people are going to these businesses and receiving experimental investigational cell-based interventions without being given a meaningful account of the lack of knowledge and evidence that they're being charged for?"

Researchers found that not only are cosmetic surgeons and naturopathic doctors offering the procedures, but that so-called pioneers of the method are training others to do the same, according to the release.

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Turner and Knoepfler also warned that this rising trend may compel fewer people to engage in stem cell tourism and instead seek these possibly risky treatments in their own neighborhood.

"In almost every state now, people can go locally to get stem cell 'treatments,'" Knoepfler, a professor at the University of California, Davis, and of the Shriners Hospital For Children. "Many people in larger metropolitan areas can just drive 15 minutes to find a clinic offering these kinds of services instead of, say, traveling to Mexico or the Caribbean. I think this reflects a change from what we've seen documented in the past and is different from what we typically think about when we think of stem cell tourism."

According to the release, Beverly Hills, California had 18 clinics— the most in the U.S.— followed by New York (14), San Antonio, Texas (13), Los Angeles (12), Austin, Texas (11), Scottsdale, Arizona (11), and Phoenix (10).

"This is a marketplace that is dramatically expanding before our eyes— we were aware early on and tracked it early on, but I don't think we knew the scope and size of the market," Turner said in the release. "Brakes ought to exist in a marketplace like this, but where are the brakes? Where are the regulatory bodies? And how did this entire industry come into being in a country where stem cell-based interventions and the medical devices that produce them are supposed to be regulated by the FDA?"