Photodynamic Therapy - Lighting Up the Treatment of Cancer

R. Alex Hsi, MD and Stephen Hahn, MD
Abramson Cancer Center of the University of Pennsylvania
Last Modified: November 1, 2001

Photodynamic therapy (PDT) is a novel approach to the treatment of cancer which holds promise as a primary or adjunctive therapeutic modality. It works by exposing a photosensitizing drug to specific wavelengths of light in the presence of oxygen. When this reaction occurs, the normally innocuous photosensitizing drug becomes cytotoxic via an activated species of oxygen, known as "singlet oxygen." The observation that these drugs are preferentially retained by tumor cells makes them an ideal agent for anti-cancer treatment.

PDT has been tried since the 1970's with mixed success. The main drawback was the lack of good photosensitizing drugs with tolerable side effects. However, in the past few years, there has been an explosion of new drugs that have been developed with better side effect profiles. In addition, these newer drugs are activated at higher wavelengths of light (in the near infrared region of the UV spectrum) which allows for deeper tissue penetration and thus more effective tumor cell killing. Armed with an array of different drugs with a spectrum of light absorbing characteristics, as well as improved laser technology to deliver the light, oncologists have more flexibility to treat a multitude of different cancers throughout the body. Among the possible targets for PDT are tumors of the brain, head and neck, breast, esophagus, lung, pleural cavity, ovary, abdominal cavity, bladder, prostate, cervix and skin.

Currently, PDT has been approved by the FDA to treat obstructing esophageal tumors, microinvasive lung cancer, and obstructing lung cancer. At the University of Pennsylvania, under the direction of Drs. Stephen Hahn, Jim Metz, and Eli Glatstein, a major project has been launched to investigate the applications of PDT on the basic science and clinical level. A treatment program for obstructing esophageal tumors as well as a Phase II study of disseminated intraperitoneal malignancies are already underway. The intraperitoneal study includes patients with recurrent or persistent ovarian cancer, sarcoma or gastrointestinal malignancies who have failed standard treatment regimens. Clinical trials for mesothelioma and malignant pleural effusions are also underway. A protocol for treating patients with locally recurrent prostate cancer after radiotherapy will begin in the year 2000. In the laboratory,studies to address various technical questions of drug and light delivery are being examined.

As this technique is developed and refined, we believe PDT may provide a new and potent weapon in the fight against cancer.