Photodynamic light therapy

For mesothelioma patients, there is a potential new treatment option involving photodynamic therapy.

What is photodynamic therapy?

Photodynamic therapy uses a laser that produces light at a specific wavelength and a chemical called a photosensitizing agent in a three step process:

(1) patients are given a photosensitizing chemical that makes cells very sensitive to light, such as photofrin®, Levulan®, Metvixia®;

(2) their cells take it up within hours (4-72 hours, usually) and become sensitive to light; and

(3) a physician shines a special laser on the tumor nodule, the chosen wavelength of light activates the chemical in the cells, and the cells die.1

Other names for photodynamic therapy include photoradiation therapy, phototherapy, or photochemotherapy. Photodynamic therapy is abbreviated as PDT.

Advantages of PDT

PDT treatment has the following advantages:

  • no reported long-term side effects,
  • little or no scarring,
  • less expensive than many current protocols,
  • repetitive treatment still beneficial (assuming the patient does not develop an allergy), and
  • usually less invasive than surgery. The laser can be inserted down an endoscope for esophageal cancer, or through a bronchoscope to view the bronchi or air passageways in the lungs.

Disadvantages of PDT

The sensitizing drug needs to be activated by light so phototherapy can only treat localized tumors that can be targeted by a light beam. Tumors with relatively few layers of cells or areas where all or most of the visible tumor has been removed (resected tumor bed) are more sensitive to PDT usually.

All cells absorb the sensitizing chemical so the skin and the eyes also become very sensitive to light. Even some indoor lights can damage the skin and eyes of people treated with the photosensitizing chemical. Third degree sunburn can develop within minutes in direct sunlight.2

Patients become sensitive to light for 5-6 weeks so they need to dress with tightly woven long sleeve shirt, long pants, broad brim hat, socks, gloves, and sunglasses to avoid getting bad sunburn. Sunscreen can not protect patients from sunlight because sunscreen only blocks ultraviolet light and the sensitizing agent (photofrin®, etc) are activated by other wavelengths not blocked by sunscreen.2

A few people develop an allergy to the sensitizing drug.

What cancers has PDT successfully treated?

Phototherapy is best suited to treat local cancer lesions. FDA has approved Photophrin® and phototherapy for treatment of cancer of the esophagus, Barrett esophagus (non cancerous lesions that may soon transform), and endobronchial cancer. Endobronchial cancer is a type of non-small cell lung cancer that grows in the lining of the airways.

In a retrospective study, esophageal cancer patients who received photodynamic therapy as a first line therapy survived longer on average (50.9 months) than those who received other options first (17.3 months).3

Cai et al reported that multiple consecutive PDT treatments of patients with stage II to stage IV bronchial lung cancer decreased the obstruction from 90% to 17% on average.4 Most patients improved significantly (partial + complete response rate was 87%).4 The patients’ quality of life improved greatly.

Photodynamic therapy is being studied as a treatment for many localized cancers— cancers that have not yet spread to other parts of the body. The types of localized tumors include cancers of the bile duct, bladder, brain, cervix, mouth, pancreas, prostate, vagina, or the vulva.

How is PDT being used to treat mesothelioma?

Dr. Glatstein from University of Pennsylvania has been using PDT along with lung-sparing surgery for many years.5 Patients with mesothelioma of the epithelial type and treated with lung-sparing surgery and PDT survived longer on average (41.2 months) than those with a nonepithelial type (6.8 months).5

The National Cancer Institute has funded Dr. Glatstein’s program project on the use of PDT in mesothelioma. Basically, it funds a clinical trial of 102 patients with mesothelioma and seeks answers to several basic questions on how PDT works:

  • Does PDT improve overall survival of radical pneumonectomy?
  • Does PDT improve the quality of life after radical pneumonectomy?
  • Does PDT affect the blood vessels feeding the tumor bed? If so, how? Can it be improved?
  • How does PDT kill the tumor cells? Do the dead cells increase the anti-tumor immune response?
  • Does inflammation help or hinder PDT therapy?

What does this mean for the future of mesothelioma treatment?

These results will help determine the benefits and risks of combining PDT with radical pneumonectomy. Depending on the results, this research may spur additional medical centers to offer the option of combining radical pneumonectomy with PDT.