What I gathered from the photodynamic therapy article is that they inject you with a substance, this substance is sucked up by the cells as it binds with O2 - then after the cell has metabolized it they hit it with a light source that in combination with the subject kills the cancer cells. It has NO damaging side effects. But is dependent on the location of the tumor - in relation to the ability of the light to reach it. It does make you photosensitive for a bit, but a good sunscreen is a simple solution along with a hat and appropriate dress.
hugs.