I have been reading a book, The Man Who Wouldn't Die, that satirizes Silicon Valley and the venture-capital start-up culture. It's reasonably funny. I was reminded, however, that sometimes culture is crazy.

At one point a character casually describes how stem-cell therapy is obviously going to make 50-year-olds feel like 20-year-olds. Grow a new liver and you're good to go, so to speak! The author clearly meant the idea as a joke. However, that idea is out there and taken seriously. Stem cells made national headlines in the late '90s and early 2000s because of some scientific breakthroughs and their promise for future medical treatments.

Just about all of our body is made up of specialized cells. These are cells that have grown to perform some specific function. Some examples are heart muscle cells, say, or red blood cells.

Stem cells are different; they have not yet specialized. That is, they have not developed many of the specific properties that are unique to the different parts of our bodies.

Given the right environment the right chemicals, for examplethey can grow into specialized cells.

There are, of course, all sorts of important details for how stem cells grow, when they specialize and how much flexibility they have in specializing. Somehow, however, there is now an industry that has skipped all that work and is marketing stem cells as a general cure. Alzheimer's disease and joint pain are frequently mentioned. If that makes you suspicious that these clinics are targeting the elderly, you would be right.

A typical treatment involves taking stem cells from a patient's bone marrow or fat and injecting it back into a sore knee or hip or whatever needs fixing. The idea, somewhat vaguely, is that the stem cells will grow to replace whatever is worn down by age.

As is true of all good scams, this one has a good story, one that can pass as proven medicine for many patients. The treatment also benefits by treating a problem with symptoms that can come and go irregularly, so a patient can honestly claim that they recovered in, say,six months.

The body is a complicated machine. It is hard to predict what will cure or not cure any specific problem. Just because a story involving stem cells sounds reasonable is not a sufficient reason to try something.

For a typical patient, we should have good, strong, positive evidence that a treatment will help. A good story is not strong, positive evidence. In the language of science, it is a hypothesis. Potentially true.

It is worth remembering that many, many things are potentially true. We don't try them all out on ourselves when we are sick.

Many of these ideas have in fact been tested in rigorous, peer-reviewed studies. So far, the evidence for positive effects is weak.

One reason these clinics have managed to skirt the rules is that extracting material from a patient then reinjecting requires less oversight for safety. Depending on the details, this treatment is considered, for Food and Drug Administration regulations, something like plasma donation (where blood is extracted, platelets removed, then reinjected into the body).

Just because a process may be safe does not make it good medicine. Medicine is not and should not be a free market. Patients will almost never have enough knowledge to reasonably choose between treatment options.

The FDA is the federal agency in charge of ensuring companies do not offer useless or harmful procedures. Unfortunately, in 2017 the FDA decided to allow stem cell clinics a three-year grace period to describe their procedures for the FDA's evaluation. As a result of that open window, hundreds of clinics have opened nationwide, offering services for which there is no strong evidence.

In the past year the FDA has realized where the industry has gone with this treatment and begun trying to crack down. Some clinics have unsafe procedures; others are misleading patients about treatments. Many clinics are still operating, unfortunately, and it can be difficult for typical patients to recognize the difference between these treatments and proven remedies. Furthermore, these bad actors could potentially make people skeptical of stem cell-based technology entirely.

That would be a shame because there is still great promise for stem cells. That may be cold comfort for those who want a treatment immediately, but that desire is the exact motivation that has led to terrible medicine for centuries.

Christer Watson, of Fort Wayne, is a professor of physics at Manchester University. Opinions expressed are his own. He wrote this column for The Journal Gazette, where his columns normally appear the first and third Tuesday of each month.

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