PHOTOFRIN-MEDIATED PHOTODYNAMIC THERAPY OF CHEMICALLY-INDUCED PREMALIGNANT LESIONS AND SQUAMOUS-CELL CARCINOMA OF THE PALATAL MUCOSA IN RATS

Photodynamic therapy (PDT), an experimental cancer therapy, was studie d in an animal model of chemically-induced epithelial dysplasia and sq uamous cell carcinoma. PDT was performed 24 hours after i.v. injection of 2.5 mg/kg bw Photofrin, and using 100 J/cm(2) incident light at tw o activation wavelengths (514.5 nm or 625 nm). Two days after PDT, the majority of rats macroscopically showed a marked erythema of the enti re palatal region. Microscopically all the rats showed oedema, haemorr hage, and necrosis of the epithelium of the intermolar area. The long- term results were not so favourable. No evidence of disease was found in 6 out of 20 rats in the 514.5 nm group and in 2 out of 20 rats in t he 625 nm treated group. Epithelial dysplasia was found in 14 out of 2 0 rats in the 514.5 nm group, and in 18 out of 20 rats of the 625 nm t reated group. Squamous cell carcinomas were found in 4 out of 20 rats treated with 514.5 nm and in 7 out of 20 rats in the 625 nm treated gr oups. Comparing both treatment wavelengths, better results were obtain ed in the 514.5 nm groups as this wavelength gave less normal tissue d amage. Based on the results of this study the application of PDT for t he treatment of field cancerization and squamous cell carcinoma of the oral cavity, is discussed.