Porphyrin fluorescence and photosensitization in head and neck cancer

Indistinct margin demarcation and autofluorescence are problems in fluorescence delineation of porphyrin-containing head and neck squamous cell cancer (HNSCC). We studied the time course and in vivo localization of porphyrin fluorescence in a squamous cell cancer hamster model and in human HNSCC. After intravenous injection, a gradient in fluorescence intensity developed rapidly until tumors fluoresced above a lower-intensity mucosal background. Hamster tumor and ulcerated HNSCC without porphyrin injection demonstrated autofluorescence grossly indistinguishable from fluorescence in porphyrin-injected tumors. However, fluorescence microscopy revealed autofluorescence to be a surface phenomenon and showed injected porphyrin localized in tumor stroma. We conclude that autofluorescence must be considered when interpreting porphyrin fluorescence. In addition, empirically designed photodynamic therapy can be effective in selected HNSCC. Data from animal experiments provide useful guidelines for the delivery of this therapy.