British retiree David Butler was surprised to find that he had prostate cancer, and that it had spread to the lymph nodes and other places near the prostate.

“I had literally no symptoms apart from needing to pee more quickly whenever I did go to the toilet,” Butler, 77, said in a news release. “Had I not told my (doctor) about it, I might not have caught my cancer until it was much further down the line.

But Butler is cancer-free now, thanks to a glowing dye that sticks to prostate cancer cells.

The fluorescent dye essentially gives doctors a “second pair of eyes” during prostate cancer surgery, helping surgeons find and remove all of a man’s cancer in real-time, researchers reported June 10 in the European Journal of Nuclear Medicine and Molecular Imaging.

The dye identified areas of cancerous tissue not picked up by the naked eye or other clinical methods in 23 men who underwent prostate surgery, including Butler, researchers report.

Thus, doctors were able to remove all the cancer, which could reduce its changes of coming back, results show.

The surgeons also avoided taking healthy tissue, reducing the risk of side effects following surgery.

“It’s the first time we’ve managed to see such fine details of prostate cancer in real-time during surgery,” lead researcher Dr. Freddie Hamdy, a professor of surgery at the University of Oxford, said in a news release.

“With this technique, we can strip all the cancer away, including the cells that have spread from the tumor which could give it the chance to come back later,” he said. “It also allows us to preserve as much of the healthy structures around the prostate as we can, to reduce unnecessary life-changing side-effects like incontinence and erectile dysfunction.”

The dye works by latching onto a protein called Prostate-Specific Membrane Antigen, which is commonly found on the surface of prostate cancer cells.

The cancer cells glow when exposed to a special kind of light, allowing surgeons to see the edges of the tumor and find any clusters of cells that have spread into nearby areas, researchers said.

Butler, a resident of Southmoor in Oxfordshire, England, underwent prostate surgery using this new technology in January 2019.

Five years later, he is fully recovered and has been cancer-free ever since.

“I retired early to make the most of life’s pleasures – gardening, playing bowls and walking,” Butler said. “Taking part in (this) study has allowed me to have many more of those pleasures for years to come.”

This marker dye could also be used for other types of cancer, by changing the target protein it uses to cling to cancer cells, researchers noted.

The dye is still in its early stages of development, and more clinical trials are underway in larger groups of patients to see if surgery using the dye outperforms standard prostate procedures, researchers said.

“Surgery can effectively cure cancers when they are removed at an early stage. But, in those early stages, it’s near impossible to tell by eye which cancers have spread locally and which have not,” Dr. Iain Foulkes, executive director of research and innovation at Cancer Research UK, said in a news release. Cancer Research UK funded the study.

“We need better tools to spot cancers which have started to spread further,” he continued. “We hope that this new technique continues to show promise in future trials. It is exciting that we could soon have access to surgical tools which could reliably eradicate prostate and other cancers and give people longer, healthier lives free from the disease.”