Photodynamic therapy uses drugs which cause cells to become sensitive to a particular type of light wavelength. When the cells containing the drug are exposed to light, they turn into a form of oxygen and destroy neighboring cells. Photodynamic therapy can be very effective in treating various medical problems including cancers like mesothelioma.
What Happens During Photodynamic Therapy?
The first step of photodynamic therapy involves patients being administered a photosensitizing agent which is a drug. There are a couple of drugs approved for use in this procedure. A photosensitizing agent, or light-sensitive drug, does exactly what the name implies – it makes cells sensitive to a certain wavelength of light. For mesothelioma, the photosensitizing agent will be administered intravenously. For some conditions, such as skin cancer, the agent may be applied topically.
Once the photosensitizing agent is in the bloodstream, it will travel throughout the body and be absorbed by cells. The agent is more readily absorbed by cancer cells and also remains in them for a longer period of time. Thus, the period of time from injection to the light treatment is very important. By the time the light treatment is given, most of the photosensitizing agent will be out of the healthy cells but the agent will still be present in the mesothelioma cells. Typically, 24-72 hours must pass before patients proceed to the next step of the therapy.
The next step of the therapy simply involves a doctor shining a light at the infected area. This is often done non-invasively through the skin’s surface. The light is of a specific wavelength which triggers the photosensitized cells to make a type of toxic oxygen. The toxic oxygen then destroys neighboring cells. The light used is often a laser light but other types of light are used too. The wavelength choice determines how far the light goes into the body through the skin.
Photodynamic therapy actually leads to acute inflammation instead of immunosuppression which is the goal of chemotherapy, surgery or radiotherapy. Photodynamic therapy also leads to invasion of the tumor.1
During this second step, patients may feel a burning sensation or pain. A pain killer may be administered before the procedure to reduce pain. Cold water may also be applied simultaneously to the area of treatment to minimize burning.
Advantages and Disadvantages of Photodynamic Therapy
The main advantage of photodynamic therapy is that it can be non invasive and non toxic. However, its applications for treating mesothelioma are very limited. It can only be used effectively if the mesothelioma has not spread from its origin. Also, because the light beam must be able to reach the tumor, the tumor must be located close to the surface of the skin – approximately 1/3 inch from the surface. The light may also not be able to penetrate into the cores of larger tumors. If the tumor is located far within the body, then the procedure may be minimally invasive; an endoscope may be inserted into the body through an incision to deliver the light.
There have been studies reporting superior results when photodynamic therapy is combined with radical pleurectomy compared to photodynamic therapy combined with modified extrapleural pneumonectomy.2 In other words, when used with other types of cancer the photodynamic therapy effectiveness is greatly increased.
Side Effects of Photodynamic Therapy
Photodynamic therapy is generally considered very safe, particularly because it focuses on such an isolated area of the body. However, there is still the risk that healthy cells will be destroyed along with the cancerous cells during the treatment. These cells will generally repair themselves without any complications.
There are several side effects associated with photodynamic therapy for mesothelioma. Patients are generally very sensitive to light (including strong indoor lights) for about six weeks after the procedure. After photodynamic treatment, patients may have a mild burn on the treated area. Inflammation, scarring and pains may also occur. Other side effects are related to the area which was treated. With pleural mesothelioma, side effects of photodynamic therapy can include breathlessness, pain during breathing, troubles swallowing, and coughing. These effects generally diminish soon after treatment.3
Though photodynamic therapy has limited use currently, researchers are studying ways it can be used more effectively, and especially in areas like the peritoneal cavity. Since mesothelioma occurs in the abdomen in some cases, it’s quite possible that research advances will be use more extensively in the future. Improvements to this procedure will include better drugs and more sophisticated equipment.
1 Castano, A. P., Mroz, P., and Hamblin, M. R. (July 2006) Photodynamic therapy and anti-tumour immunity. Nat Rev Cancer, v6:7, 535-545, doi: 10.1038/nrc1894.
2 Friedberg JS, Mick R, Culligan M, Stevenson J, Fernandes A, Smith D, Glatstein E, Hahn SM, Cengel K. (June 2011) Photodynamic therapy and the evolution of a lung-sparing surgical treatment for mesothelioma. Ann Thorac Surg, c91:6, 1738-1745.
3 Hahn, S. M., Smith, R. P. and Friedberg, J. C. Photodynamic therapy for mesothelioma. (Jan 2011) Current Treatment Options in Oncology, v2:5, 375-373.