Tumour-zapping lasers are being deployed on another front of the war against cancer. A new study shows they can help to stop a cancer from spreading by destroying the lymphatic vessels that act as highways for the mutant cells.

In Photodynamic therapy, or PDT, doctors inject a light-sensitive drug into tumours near the skin’s surface and then turn an infrared laser on it. The light encourages the drug to produce a form of oxygen that destroys cancer cells.

The therapy is already used to precisely target several types of cancer tumour. But by using it on nearby vessels instead, Tuomas Tammela and his colleagues at the University of Helsinki in Finland think that PDT might help to stop cancer spread in its tracks.

Cancer spread, or metastasis, occurs when tumour cells enter lymph or blood vessels. Metastasis exploits lymphatic vessels’ normal function of draining fluid from the body’s tissues, removing bacteria and returning the fluid to the bloodstream. Tumours can sprout their own lymph vessels to further aid the dispersal of cancer cells.


Lighting lymph

To halt cancer spread through the lymphatic system, Tammela’s team simply destroyed the lymphatic vessels near the tumour.

They began by injecting the ears of mice with cancer cells and waiting for tumours to develop. They then chose a light-sensitive drug – verteporfin – that is an ideal size to squeeze into the lymphatic vessels and injected it under the skin of the ears of the mice. Two days later the team confirmed that verteporfin had been taken up by the lymph vessels around the tumours by shining ultraviolet light on the area, which makes the drug glow green.

“Almost all collecting lymphatic vessels of the mouse ear could be filled with verteporfin after three to four injections,” the researchers report.

When the team then shone an infrared laser on the injected ear, they were able to destroy all of the lymphatic vessels in the region – as well as the cancer cells in the tumour. A day after treatment, only one of eight mice had any trace of cancer remaining.

“Metastasis is the major clinical problem with cancer,” says Steven Stacker at the Peter MacCallum Cancer Centre in Melbourne, Australia, who was not involved with the study. “The study certainly paves the way for thinking about how this could be applied in human subjects.”

Journal reference: Science Translational Medicine, DOI: 10.1126/scitranslmed.3001699