Tumor cells in transit along a laser-lit cancer highway

Scientists used laser light to destroy cancer cells in lymphatic vessels, stopping their spread from tumors to lymph nodes.
Written by Janet Fang, Contributor

Scientists used infrared laser light to destroy cancer cells lodged in lymphatic vessels, stopping the spread of tumor cells – in mouse ears and pig hooves, for now.

Vessels in the lymphatic system drain fluids and cells from our tissues. As such, they act like a highway for cancer cells to spread from the tumor to distant tissues (or to metastasize). Tumors even produce factors that help make new lymphatic vessels.

The current treatment is to surgically remove the primary tumor and the metastatic lymph nodes. But tumor cells in-transit inside the lymphatic vessels have been ignored, resulting in relapse.

So Tuomas Tammela of the University of Helsinki and colleagues experimented with a laser technique – called photodynamic therapy (PDT) – that uses light and light-activated drugs to kill clumps of tumor cells in the cancer highway.

  1. They injected a light-sensitive drug called verteporfin into tumors.
  2. Using an infrared laser light, they illuminated the tissues of the lymphatic system.
  3. This, in effect, turned the cytotoxic drug on, causing the lymphatic vessels to shrink, fragment, and become leaky.

After photodynamic therapy, the team found that the rate of lung cancer relapse was reduced from 65% to 10%. Combined with current surgical methods, this targeting of in-transit cells may reduce the rate of cancer recurrence in humans.

“PDT could easily be combined with existing surgical techniques to destroy the lymphatic vessels draining from the tumor,” Tammela says, “as well as the tumor cell aggregates residing within them.”

PDT using verteporfin is already being used clinically to destroy overgrown blood vessels in the retina of patients with macular degeneration, a leading cause of blindness. According to Tammela, since both the drug and the PDT concept are already in use in patients, they’re more likely to receive regulatory approval for targeting tumor-associated lymphatic vessels in cancer patients undergoing surgery than drugs still in earlier phases of development.

The study was published in Science Translational Medicine yesterday.

Image: Lymphatic vessel (purple) filled by cancer cells (green) that have escaped the primary tumor / Helena Schmidt and Toumas Tammela

Schematic of technique:

This post was originally published on Smartplanet.com

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