Mesothelioma Photodynamic Therapy

The potential success of photodynamic therapy runs off the principle that normal cells and cancer cells react differently to photosensitizing drugs. Photodynamic therapy uses light energy to destroy cancer cells while leaving healthy cells largely unaffected.

During the photodynamic therapy treatment process a patient is given drugs called photosensitizers, which make cells sensitive to light. The treated cells are then exposed to light of a specific wavelength, and this causes them to produce a particular form of oxygen that is toxic and kills nearby cancer cells.

Photodynamic therapy begins with the injection of a photosensitizing drug. This drug is administered intravenously into the bloodstream and over a period of 24 to 72 hours the drug travels throughout the body and is absorbed by cells.

In general, cancer cells absorb the photosensitizing drug quicker than healthy cells. In addition, the drug remains in cancer cells longer than healthy cells. For these reasons, by the time the patient proceeds to the next stage of treatment, the drug is predominately present in cancer cells with low concentrations remaining in some healthy cells.

After the drug administration phase, the patient is treated with light of a specified wavelength that reacts to the photosensitizing drug present in cancer cells. A physician simply shines a beam of light on the affected area, which may last anywhere from a few minutes to an hour. During treatment, cancer cells absorb the light, which causes them to produce a form of oxygen that is highly reactive. The oxygen eventually enters nearby cancer cells and damages them, resulting in death of the affected cells. In addition, photodynamic therapy can also destroy cancer cells by damaging blood vessels that are present in tumors, thus preventing cancer cells from absorbing nutrients.

Photodynamic therapy is usually performed on an out-patient basis, and is often used in conjunction with other types of treatment, such as surgery and chemotherapy. Due to the nature of this mesothelioma treatment, it is not effective for the treatment of cancer that has spread extensively throughout the body. Photodynamic therapy is most effective in treating single, localized cancers.

Some drugs used in photodynamic therapy can make the eyes and skin very sensitive to light for up to six weeks after treatment. If the skin and eyes are not protected, they can become burned or blistered after just a few minutes of exposure to sunlight or bright indoor lights. For this reason, those undergoing photodynamic therapy are advised to avoid bright indoor lights and direct sunlight for six weeks or longer after treatment.

Damage to normal, healthy tissue is minimal when photodynamic therapy is used because the treatment is highly specific. In some cases, the treatment may cause burns, pain, scarring, and swelling in nearby healthy tissue, as well as side effects such as coughing, shortness of breath, trouble swallowing, painful breathing, and stomach pain, depending on the location of treatment.

Because the type of light used in photodynamic therapy cannot penetrate deeply into skin and tissue it is most effective in cancers that affect the skin, or for cancers that are near the skin's surface (including some types of lung cancer). In addition, individuals with large tumors may not be suitable candidates for photodynamic therapy, as the light is unable to penetrate throughout the tumor.

Medical research for photodynamic therapy seeks to increase the range of cancers for which the treatment can be used (including peritoneal mesothelioma) and to improve the efficacy of the therapy for treating larger tumors. Other research concentrates on the possibility of administering photodynamic therapy during surgery, or by means of optical fibers that are guided directly into tumors.