When light (hv) is delivered to a photosensitizer (PS)-loaded tumour it induces both apoptotic and necrotic cell death. These cells are phagocytosed by dendritic cells (DCs) that have accumultated owing to the acute inflammatory response which is triggered by photodynamic therapy (PDT). DCs mature after stimulation by cytokines, which are released at the site of inflammation, and home to the regional lymph nodes where they present antigens to the T lymphocytes. Activated T lymphocytes become effector T cells and, attracted by chemokines, migrate to the tumour and kill the tumour cells.
Photodynamic therapy (PDT)is a cancer treatment that uses a drug, called a photosensitizer or photosensitizing agent, and a particular type of light. When photosensitizers are exposed to a specific wavelength of light (such as from a laser), they produce a form of oxygen that destroys nearby cells.
PDT is approved by the United States Food & Drug Administration (FDA) for the treatment of both early and late-stage lung cancer. Other countries have approved PDT for treatment of various cancers as well. Unlike chemotherapy, radiation, and surgery, PDT is useful in treating all cell types, whether small cell or non-small cell carcinoma.
What's so great about PDT?
One of the main advantages of PDT in lung cancer is that it works quickly. For example, a person with a tumor blocking a major airway may get relief in a few days. Another plus is that PDT can work in places where surgery would not be feasible, such as the trachea, the major airway leading from the voice box to the lungs.
How it works ?
Another advantage is that PDT can be repeated a number of times, unlike radiation and chemotherapy. This feature allows physicians to repeatedly treat tumors and control their growth.
PDT has few side effects. The most common side effect is photosensitivity, or sensitivity to bright light. The period of photosensitivity varies from drug to drug. With the only FDA-approved drug in the United States, Photofrin®, photosensitivity lasts 4-6 weeks. Patients must protect their skin from bright light during this period.
What's the downside?
As with all medical treatments, there are limitations to what PDT can do. The tumor has to be located in a place where it can be accessed with the bronchoscope, the flexible tube inserted through the mouth and into the lungs to see the tumor and shine light on it.
Devices for implanting optical fibers to deliver laser light to tumors lying deep within the body are in development. However, regular clinical use of these devices is a few years away.
Red light is used for PDT because it penetrates more deeply into tissue than other colors or wavelengths. Still, the red laser light used for PDT can only go so deep before it is absorbed by the tissue or scattered too much to be therapeutic. PDT penetrates into tissue to a depth of about one-half to one centimenter (about 1/4 inch). Two or three laser light treatments are often needed to shine light on the deeper parts of a thick tumor.
Research is being done to find ways to increase the depth of penetration with new photosensitizing drugs and different wavelengths of light.
What are the side effects?
The major side effect of PDT is photosensitivity, or sensitivity to light. Most people find this inconvenient, but not intolerable. The photosensitizing drug currently used for PDT stays in the skin for about 4-6 weeks. During this time period, the patient must be careful not to get too much exposure to bright light, such as sunlight, or the bright overhead light in a dentist's office. A gradual increase in bright light exposure neutralizes or "bleaches" the drug slowly, and photosensitivity diminishes. As this occurs, many people develop temporary skin darkening, much like having a suntan. If you are a PDT patient, be sure to ask your health care provider about photosensitivity.
Pain is another side effect of PDT. As the diseased tissue breaks down, it causes inflammation which can cause pain. Fortunately, the pain of PDT is usually mild to moderate and is easily controlled .
A third side effect of PDT for lung cancer is shortness of breath. This occurs from fluid buildup in the lungs after PDT. It is also caused by the inflammation that occurs as diseased tissue (tumor) is broken down and removed from the body. Mild shortness of breath is expected, but if you have any concerns about feeling short of breath, please phone your health care provider promptly.
The good news about the side effects of PDT is that they are usually easily managed and temporary. There is no cumulative damage to organs or healthy tissues, as occurs with radiotherapy (radiation) or chemotherapy.
The Future of PDT
Investigations are underway for treating many different types of diseases in various parts of the body. Only time will tell how many uses medical science finds for PDT. New types of light delivery devices and new photosensitizing drugs will expand the usefulness of PDT in the future. Investigations are underway into using PDT to treat skin disease, brain tumors, gynecological cancers, and other conditions.
The National Cancer Institute occasionally has clinical trials on PDT
REFERENCES AND SOURCES
2. Cancer treatments centers of America
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