Scientists just completed a trial of a new, non-surgical prostate cancer treatment that uses a tumour-killing drug based on ocean bacteria, and the procedure saw almost half the patients go into complete remission.

The treatment is known as vascular-targeted photodynamic therapy (VTP), and is made possible by a drug called WST11, which is derived from bacteria that live at the bottom of the ocean. These light-sensitive organisms convert photons into energy, and when the same trick is mimicked by WST11, the compound kills cancer cells.

In a broad clinical trial at 47 treatment sites across 10 different European countries, 49 percent of patients with early prostate cancer that were treated with VTP went into complete remission, compared with 13.5 percent in the control group.

"These results are excellent news for men with early localised prostate cancer, offering a treatment that can kill cancer without removing or destroying the prostate," says lead researcher Mark Emberton from University College London.

"This is truly a huge leap forward for prostate cancer treatment, which has previously lagged decades behind other solid cancers such as breast cancer."

Men diagnosed with early or low-risk prostate cancer are usually monitored via regular testing to make sure the cancer isn't spreading.

But if it does begin to spread, patients face a dilemma, as traditional treatments such as surgery or radiation therapy can cause lifelong erectile problems and incontinence.

For these reasons, a non-surgical treatment that doesn't come with such negative side effects has long been a goal of researchers, and VTP with WST11 could be it.

In the study, the procedure only caused short-term urinary and erectile problems, which had resolved within three months, and all other side effects disappeared within two years.

"This changes everything," Emberton told James Gallagher at the BBC.

"Traditionally the decision to have treatment has always been a balance of benefits and harms. … To have a new treatment now that we can administer, to men who are eligible, that is virtually free of those side effects, is truly transformative."

The treatment involves injecting WST11 into the bloodstream, and inserting optical fibres into the prostate gland.

When the optical fibres are turned on, light beams activate the drug in the patient's blood, causing it to release high-energy free radicals that destroy tumour tissue while leaving surrounding tissue unharmed.

Of the individuals who took part in the trial, cancer progressed in 58 percent of men in the control group, who maintained regular monitoring during the study. But for the men who received VTP, only 28 percent saw tumours spread.

According to Emberton, these results would be even stronger today, as the researchers in the trial didn't have access to the latest MRI technology when they began their study in 2011.

"We can now pinpoint prostate cancers using MRI scans and targeted biopsies, allowing a much more targeted approach to diagnosis and treatment," Emberton said in a press release.

"This means we could accurately identify men who would benefit from VTP and deliver treatment more precisely to the tumour. With such an approach, we should be able to achieve a significantly higher remission rate than in the trial and send nearly all low-risk localised prostate cancers into remission."

There's also scope to extend the procedure to other cancers, including breast and liver cancer, but first the researchers need to continue monitoring the patients who took part in this trial and see if the remission rates hold up over time.

Meanwhile, the European Medicines Agency (EMA) is currently reviewing the treatment, but it could be years before it's made available to patients in the broader population.

It's important to note that there's still a lot we don't know about this treatment, and despite its early promise, it's not necessarily more effective than surgery or radiation therapy at removing the danger of cancer.

That said, it also doesn't seem to offer the same kinds of complications, so depending on how further research pans out, it could be a valid avenue of treatment in the future.

One man who hopes the wait isn't too long is Gerald Capon, a 68-year-old from West Sussex in the UK, who took part in the study.

"[T]he trial changed my life. I'm now cancer-free with no side effects and don't have to worry about needing surgery in future," he says.

"I feel so lucky to be in this position… I hope that other patients will be able to benefit from this treatment in future."

The findings are reported in The Lancet Oncology.