What are the limitations of PDT?
The light needed to activate most photosensitizers cannot pass through more than about one-third of an inch of tissue (1 centimeter). For this reason, PDT is usually used to treat tumors on or just under the skin or on the lining of internal organs or cavities (3). PDT is also less effective in treating large tumors, because the light cannot pass far into these tumors (2, 3, 6). PDT is a local treatment and generally cannot be used to treat cancer that has spread (metastasized) (6).
Does PDT have any complications or side effects?
Porfimer sodium makes the skin and eyes sensitive to light for approximately 6 weeks after treatment (1, 3, 6). Thus, patients are advised to avoid direct sunlight and bright indoor light for at least 6 weeks.
Photosensitizers tend to build up in tumors and the activating light is focused on the tumor. As a result, damage to healthy tissue is minimal. However, PDT can cause burns, swelling, pain, and scarring in nearby healthy tissue (3). Other side effects of PDT are related to the area that is treated. They can include coughing, trouble swallowing, stomach pain, painful breathing, or shortness of breath; these side effects are usually temporary.
What does the future hold for PDT?
Researchers continue to study ways to improve the effectiveness of PDT and expand it to other cancers. Clinical trials (research studies) are under way to evaluate the use of PDT for cancers of the brain, skin, prostate, cervix, and peritoneal cavity (the space in the abdomen that contains the intestines, stomach, and liver). Other research is focused on the development of photosensitizers that are more powerful (1), more specifically target cancer cells (1, 3, 5), and are activated by light that can penetrate tissue and treat deep or large tumors (2). Researchers are also investigating ways to improve equipment (1) and the delivery of the activating light (5).
1. Dolmans DE, Fukumura D, Jain RK. Photodynamic therapy for cancer. Nature Reviews Cancer 2003; 3(5):380–387.
2. Wilson BC. Photodynamic therapy for cancer: principles. Canadian Journal of Gastroenterology 2002; 16(6):393–396.
3. Vrouenraets MB, Visser GW, Snow GB, van Dongen GA. Basic principles, applications in oncology and improved selectivity of photodynamic therapy. Anticancer Research 2003; 23(1B):505–522.
4. Dougherty TJ, Gomer CJ, Henderson BW, et al. Photodynamic therapy. Journal of the National Cancer Institute 1998; 90(12):889–905.
5. Gudgin Dickson EF, Goyan RL, Pottier RH. New directions in photodynamic therapy. Cellular and Molecular Biology 2002; 48(8):939–954.
6. Capella MA, Capella LS. A light in multidrug resistance: photodynamic treatment of multidrug-resistant tumors. Journal of Biomedical Science 2003; 10(4):361–366.
Source: National Cancer Institute