photodynamic therapy

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A type of phototherapy in which a nontoxic light-sensitive compound that has been injected into a patient is exposed selectively to light, whereupon it becomes toxic to targeted malignant and other diseased cells.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun medicine A treatment for some forms of cancer and some skin disorders, involving the use of photosensitive chemicals, and controlled and directed laser beams.