The Effect of Localized Porphyrin Photodynamic Therapy on the Induction of Tumour Metastasis

Studies were performed to determine whether localized treatment of subcutaneously growing Lewis Lung Carcinoma (LLC) in C57BL/6 mice with porphyrin photodynamic therapy (PDT) affects the formation of distant metastases. Treatments consisted of a 10 mg kg-1 dose of dihematoporphyrin-ether (Photofrin II) followed 24 h later by local tumour irradiation with 630 nm red light. Total doses of light ranged from 0-500 J cm-2 and the irradiance of delivered light was 150 mW cm-2. Primary LLC tumours were treated at a volume of 25-30 mm3, and lung metastases were determined 21 days following transplantation. Mice exposed to PDT treatment which produced either partial or complete local tumoricidal responses had significantly decreased numbers of metastatic lung colonies compared to controls. In addition, PDT treated mice had equal or less metastatic lung colonies than comparable mice treated with local surgical excision of the primary LLC lesion. These results indicate that local PDT does not enhance metastatic spread of LLC following either curative or noncurative treatments.