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Danish researchers trying to find a way to help men badly injured by prostate cancer surgery say they got mixed results with an experimental new approach: injecting them with stem cells.

Only a few of the men were helped, and those men were able to have sex after the treatment, the researchers told a meeting of urologists.

The researchers' findings suggest that men should stay away — at least for now — from clinics that already offer stem cell treatment for erectile dysfunction. CIPhotos / Getty Images/iStockphoto

The researchers' findings suggest that men should stay away — at least for now — from clinics that already offer stem cell treatment for erectile dysfunction.

But their findings also suggest that men who become impotent after prostate surgery shouldn't give up hope.

"After six months, eight of the men could initiate sexual intercourse," said Dr. Martha Haahr of Odense University Hospital.

"What we have done establishes that this technique can lead to men recovering a spontaneous erection — in other words, without the use of other medicines, injections, or implants,” Haahr added.

Related: Clinics Offer Unproven Stem Cell Treatments

Erectile dysfunction is very common, and it’s led to a booming market in drugs such as Viagra and Cialis, as well as an industry providing penis implants and other treatments.

The dysfunction is caused by a variety of factors. Heart disease and diabetes can damage the blood vessels in the penis, for example. And prostate cancer treatment can damage the nerves and blood vessels in the surrounding area.

“If it’s as effective as we think, it could help many kinds of men."

A study published earlier this month found more than half of men lost the ability to have sex after radical prostatectomy — extensive surgery done to remove a cancerous prostate. That’s more than the 40 percent or so of men treated using external beam radiation.

Related: Men Can Choose Prostate Treatments by the Side-Effects They'd Prefer

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Haahr's team worked with some of the most hard-core cases: men whose nerves had been badly damaged by prostate surgery. “We could not damage their erectile function any more than it already was,” Haahr said.

They worked with a small group — just 21 men. Each man got a single injection of his own stem cells, in this case, mesenchymal stem cells separated out from their own body fat.

If it’s done right, these procedures have been shown to be safe. The patient’s fat is removed with a syringe, processed in a lab to separate out the semi-mature stem cells, which are re-injected. Because the patient’s own cells are used and not manipulated, the Food and Drug Administration doesn’t usually regulate these procedures.

Of the 21 men, 14 were still continent; they did not have damage to their ability to control urination. Out of those 14 men, 8 regained sexual function and kept it for a year after a single stem cell injection, Haahr told the European Association of Urology.

Now the team wants to try in a larger group of men, using a placebo in some to rule out psychological effects of the treatment.

Related: All Prostate Treatments Work About Equally Well

"If it works in these men, it would also work in men with have been treated using chemotherapy and radiation," she said. It may also help men whose tissues are damaged by aging, heart disease or diabetes.

"If it's as effective as we think, it could help many kinds of men," she said.

"We are now beginning a larger, phase 2 trial to better evaluate its effectiveness and confirm its safety."

Haahr is not sure why the procedure did not help the incontinent men, but believes it could be because they had more extensive nerve damage. They may need higher or more frequent doses of stem cells, she said.

Stem cells are the body's master cells. The name's confusing because there are many different types. So-called adult stem cells are found throughout anyone’s body and they are partly differentiated, starting down the pathway to a specific tissue type.

“This new option would be welcome if would give some return to function."

Mesenchymal stem cells are destined to become muscle, fat and bone tissue.

Haahr is not sure how they work but believes the cells are finding their way to damaged areas and turning themselves into the necessary tissue, repairing the blood vessels needed to provide an erection.

"This new option would be welcome if would give some return to function. That is pretty exciting," said Dr. Daniel Barocas, a urologic surgeon at Vanderbilt University who was not involved in the study.

"If this pans out in additional validation studies it would be an exciting new option for men who don’t respond to the standard treatment."

Dr. Irwin Goldstein, director of sexual medicine at Alvarado Hospital in San Diego, says it's clear much more study is needed. But it's "definitely something people will want that can treat an embarrassing and humiliating distressing medical condition," he said.

Haahr's team is not the first to try using stem cells to restore sexual function in men, but it is still a highly experimental approach. That has not, however, stopped clinics from offering the treatments.

Related: Shock Wave Treatment May Help Erectile Dysfunction

Last year, a team of experts found more than 500 clinics offering unproven stem cell treatments for a variety of conditions. It’s easy to find clinics offering the treatments for erectile dysfunction, as well.

The FDA says there are virtually no approved stem cell treatments available as commercial products, but also says there’s no law against taking out a patient’s own cells and re-infusing them.

Earlier this month a team reported three women given "stem cell" treatments for vision loss at one Florida clinic ended up with severe eye damage.