For some types of early skin cancer, the drug is applied as a cream which can be activated by a range of sources of red light. It is widely available and gives good cosmetic results. For internal cancers, the light source is usually a laser and the drug is given by mouth or injection. PDT involves the patient taking the drug, which accumulates in the cancerous area. A laser is then used to shine light on the cancer, which activates the drug and causes local tissue destruction. Both the medicine and the laser are basically harmless until combined.
PDT is now available as a treatment option for patients with some types of cancer. And it can even lead to a cure for some people if used early enough.