How does photodynamic therapy kill cancer cells?

Photodynamic therapy kills cancer cells using a light-activated drug called a photosensitizer.

When cells that have absorbed the photosensitizer are exposed to a specific wavelength of light, the drug produces a form of oxygen, called an oxygen radical, that kills them. Because the drug tends to build up in abnormal cells and the light is aimed at them, healthy cells are largely spared.

Photodynamic therapy may also work in two other ways. It can damage the blood vessels in the tumor, which keeps the tumor from getting the blood it needs to grow. And it may trigger the immune system to attack tumor cells, even in other areas of the body.

The treatment is given in two steps: first you receive the photosensitizer, and then, after 24 to 72 hours, the tumor is exposed to the light. Your care team can explain how the light will reach your tumor.