Although literally thousands of people have been treated this way, PDT is just becoming accepted among health care providers and offered to cancer patients. This is an overview of PDT with insights into how new cancer treatments are developed and accepted by the medical community. Certain physiological properties of tumor tissue cause the photosensitizer to be retained in tumors, but excreted from most healthy tissue. When laser light of a certain wavelength is shined on the tumor, the drug contained within it is converted to an active form that creates toxic molecules, killing cancer cells. Although the drug and light together are powerful, neither has any tumor-killing effect alone.
Tumors usually shrink within one to two days of therapy.
However, the laser light can only penetrate about one centimeter, or one-quarter inch, into tissue, so large bulky tumors often require repeated light exposure. PDT has several advantages. There are no cumulative toxic effects of PDT as with radiation or chemotherapy, so the procedure can be repeated several times if needed. PDT works on virtually all types of cancer. It is not specific to the cell type of the cancer, like chemotherapy agents or radiation.