PHOTODYNAMIC THERAPY - A PROMISING NEW MODALITY FOR THE TREATMENT OF CANCER

The first reports on photodynamic therapy (PDT) date back to the 1970s . Since then, several thousands of patients, both with early stage and advanced stage solid tumours, have been treated with PDT and many cla ims have been made regarding its efficacy. Nevertheless, the therapy h as not yet found general acceptance by oncologists. Therefore it seems legitimate to ask whether PDT can still be described as ''a promising new therapy in the treatment of cancer''. Clinically, PDT has been ma inly used for bladder cancer, lung cancer and in malignant diseases of the skin and upper aerodigestive tract. The sensitizer used in the ph otodynamic treatment of most patients is Photofrin(R), (Photofrin(R), the commercial name of dihematoporphyrin ether/ester, containing > 80% of the active porphyrin dimers/oligomers (A.M.R. Fisher, A.L. Murphee and C.J. Gomer, Clinical and preclinical photodynamictherapy. Review Series Article, Lasers Surg. Med., 17 (1995) 2-31). It is a complex mi xture of porphyrins derived from hematoporphyrin. Although this sensit izeris effective, it is not the most suitable photosensitizer for PDT. Prolonged skin photosensitivity and the relatively low absorbance at 630 nm, a wavelength where tissue penetration of light is not optimal, have been frequently cited as negative aspects hindering general acce ptance. A multitude of new sensitizers is currently under evaluation. Most of these ''second generation photosensitizers'' are chemically pu re, absorb light at around 650 nm or greater and induce no or less gen eral skin photosensitivity. Another novel approach is the photosensiti zation of neoplasms by the induction of endogenous photosensitizers th rough the application of 5-aminolevulinic acid (ALA). This article add resses the use of PDT in the disciplines mentioned above and attempts to indicate developments of PDT which could be necessary for this ther apy to gain a wider acceptance in the various fields.