Topping the list of predatory business schemes, direct-to-consumer clinics peddling unproven stem cell therapies may be right up there with payday loans and Shkreli-esque drug pricing. Such clinics can tout dangerous, often exorbitantly priced “treatments.” They frequently target the vulnerable and desperate, including terminal cancer patients, parents of autistic children, and grown children of parents with Alzheimer’s or Parkinson’s disease. And the results can range from placebos to bones in eyelids and scary growths on spinal cords.

We tend to think this kind of quackery only thrives in countries with lax regulations like China, India, or Mexico. The phrase “stem cell tourism” usually evokes a plane trip. But stem cell therapies are unexpectedly flourishing in the US and may only require a short car trip.

In an analysis published this week in Cell Stem Cell, researchers identified a startling 351 businesses, encompassing 570 clinics across the US, that offer stem cell therapies largely unproven and unapproved by the Food and Drug Administration. Without peer-reviewed evidence, these businesses and clinics claim their therapies can treat dozens of diseases, injuries, and cosmetic indications, including joint pain, autism, spinal cord injuries, muscular dystrophy, and breast augmentation. Costs can reach into tens if not hundreds of thousands of dollars for treatments.

“Our analysis should serve as a valuable resource for contemporary debate concerning whether the US marketplace for stem cell interventions is adequately monitored and regulated by the FDA, the Federal Trade Commission, state medical boards, and other agencies tasked with promoting patient safety and accurate advertising,” the authors conclude.

Stem cells, some of which can differentiate into nearly any type of cell in the body, do hold enormous promise for many types of treatments. But so far, the only type of stem cell treatment that has been scientifically verified and approved by the FDA involves stem cells from bone marrow or blood that are used in transplants to treat cancers or other disorders that affect the immune system and blood. Clinics using these approved treatments may be safe and fall in line with FDA rules.

However, many clinics are likely not in that category. Seizing the scientific excitement, these clinics have made overblown or bogus claims that stem cells can treat or cure a wide variety of other ailments. And they have strayed into using several cell types. In their analysis, Leigh Turner, a bioethicist at the University of Minnesota, and Paul Knoepfler, a stem cell researcher at University of California, Davis, found clinics advertising stem cells made from patients’ fat, “placental” stem cells (of origins unknown), and cells that are likely not stem cells of any kind, as well as “bovine amniotic cells.”

So far, many of these clinics have largely escaped regulatory wrath, perhaps because in the past they mostly extracted patient cells, did some insignificant manipulation to them, and then returned them to the same patient. Procedures like these may have relatively few hazards. However, with the apparent boom of the stem cell industry, the FDA is now moving forward with a draft guidance that would classify most stem cells used in clinics as drugs, which require a tough approval process.

By spotlighting the breadth of the stem cell industry currently in the US, Turner and Knoepfler hope to help the FDA and other regulatory agencies curb the dangerous effects of unproven treatments. For instance, just last week The New York Times wrote about the case of Jim Gass, who spent hundreds of thousands of dollars to get stem cell treatments from Mexico, China, and Argentina that were said to help him recover from a stroke. When he returned to the US, surgeons found a large bloody mass of primitive cells aggressively taking over his lower spinal column. The cells did not belong to Gass. And in another case several years ago, a woman who received a stem cell-based facelift treatment from a clinic in California had to have bone fragments surgically removed from her eyelid months later.

Editor's Note: This story has been updated to clarify that not all stem cells can differentiate into nearly every type of cell in the body.

Cell Stem Cell, 2016. DOI: 10.1016/j.stem.2016.06.007