A drug activated by laser light successfully destroys early prostate cancer while avoiding side effects that commonly occur with surgery, trial results have shown.
The new technique, called vascular-targeted photodynamic therapy (VTP), involves injecting a light-sensitive drug into the bloodstream. The drug is then "switched on" by laser pulses fired through optical fibres inserted into the prostate.
Of 196 men who received the treatment, about half showed no signs of the disease two years later, compared with 13.5% of those given standard care.
Because VTP only targets prostate tumours, it does not cause the long-term problems of impotence and urinary incontinence often associated with "radical" surgery or radiotherapy.
Lead investigator Professor Mark Emberton, consultant urologist at University College London Hospital, said: "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.
"This is truly a huge leap forward for prostate cancer treatment, which has previously lagged decades behind other solid cancers such as breast cancer.
"In 1975, almost everyone with breast cancer was given a radical mastectomy, but since then treatments have steady improved and we now rarely need to remove the whole breast.
"In prostate cancer, we are still commonly removing or irradiating the whole prostate, so the success of this new tissue-preserving treatment is welcome news indeed."
Currently, men with low-risk localised prostate cancer are put under "active surveillance", which means monitoring the disease but providing no treatment unless it becomes more severe.
In the trial consisting of 413 men, participants were randomly assigned either to VTP or active surveillance.
Only 6% of the VTP group later needed radical treatment, compared with 30% of active surveillance patients. VTP treatment also doubled the average time of cancer progression from 14 months to 28 months.
The trial, reported in The Lancet Oncology journal, was conducted across 47 treatment sites in 10 European countries, most of which were performing VTP for the first time.
Prof Emberton said: "The fact that the treatment was performed so successfully by non-specialist centres in various health systems is really remarkable.
"New procedures are generally associated with a learning curve, but the lack of complications in the trial suggests that the treatment protocol is safe, efficient and relatively easy to scale up.
"We would also expect the treatment to be far more precise if we repeated it today, as technology has come a long way since the study began in 2011.
"We can now pinpoint prostate cancers using MRI (magnetic resonance imaging) scans and targeted biopsies, allowing a much more targeted approach to diagnosis and treatment.
"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.
"We also hope that VTP will be effective against other types of cancer. The treatment was developed for prostate cancer because of the urgent need for new therapies, but it should be translatable to other solid cancers including breast and liver cancer."
The drug used, WST11, is derived from bacteria at the bottom of the ocean. To survive with very little sunlight, the bugs have evolved to convert light into energy with high efficiency. This property was exploited to develop the drug, a compound that releases destructive tumour-busting "free radical" molecules when activated by laser light.
Gerald, a man aged in his sixties from Surrey, was one of the first patients to be treated with VTP under the care of Prof Emberton.
He said: "The treatment ... changed my life. I'm now cancer-free with no side-effects and don't have to worry about needing surgery in future. I feel so lucky to be in this position.
"I've met other men who had surgery - they had to stay in hospital for days whereas I could go home the next day, and one suffered from terrible incontinence which he found very distressing.
"I had some minor side-effects for a few weeks after the operation, but I'm back to normal now."
Each year, more than 46,000 men in the UK are diagnosed with prostate cancer and 11,000 die from the disease.