Photodynamic therapy (also called PDT, photoradiation therapy,
phototherapy, or photochemotherapy) is a treatment for some types of cancer.
It is based on the discovery that certain chemicals known as
photosensitizing agents can kill one-celled organisms when the organisms are
exposed to a particular type of light. PDT destroys cancer cells through the
use of a fixed-frequency laser light in combination with a photosensitizing
agent.
In PDT, the photosensitizing agent is injected into the bloodstream and
absorbed by cells all over the body. The agent remains in cancer cells for a
longer time than it does in normal cells. When the treated cancer cells are
exposed to laser light, the photosensitizing agent absorbs the light and
produces an active form of oxygen that destroys the treated cancer cells.
Light exposure must be timed carefully so that it occurs when most of the
photosensitizing agent has left healthy cells but is still present in the
cancer cells.
The laser light used in PDT can be directed through a fiber-optic (a very
thin glass strand). The fiber-optic is placed close to the cancer to deliver
the proper amount of light. The fiber-optic can be directed through a
bronchoscope into the lungs for the treatment of lung cancer or through an
endoscope into the esophagus for the treatment of esophageal cancer.
An advantage of PDT is that it causes minimal damage to healthy tissue.
However, because the laser light currently in use cannot pass through more
than about 3 centimeters of tissue (a little more than one and an eighth
inch), PDT is mainly used to treat tumors on or just under the skin or on
the lining of internal organs.
Photodynamic therapy makes the skin and eyes sensitive to light for 6
weeks or more after treatment. Patients are advised to avoid direct sunlight
and bright indoor light for at least 6 weeks. If patients must go outdoors,
they need to wear protective clothing, including sunglasses. Patients should
talk with their doctor about what to do if the skin becomes blistered, red,
or swollen. Other temporary side effects of PDT are related to the treatment
of specific areas and can include coughing, trouble swallowing, abdominal
pain, and painful breathing or shortness of breath.
In December 1995, the U.S. Food and Drug Administration (FDA) approved a
photosensitizing agent called porfimer sodium, or Photofrin-R, to relieve
symptoms of esophageal cancer that is causing an obstruction and for
esophageal cancer that cannot be satisfactorily treated with lasers alone.
In January 1998, the FDA approved porfimer sodium for the treatment of early
nonsmall cell lung cancer in patients for whom the usual treatments for lung
cancer are not appropriate. The National Cancer Institute and other
institutions are supporting clinical trials (research studies) to evaluate
the use of photodynamic therapy for several types of cancer, including
cancers of the bladder, brain, larynx, and oral cavity. Researchers are also
looking at different laser types, photosensitizers that can be applied to
the skin to treat superficial skin cancers, and new photosensitizing agents
that may increase the effectiveness of PDT against cancers that are located
further below the skin or inside an organ.
This fact sheet was reviewed on 8/24/99
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