Selective distribution of porphyrins in skin thick basal cell carcinoma after topical application of methyl 5-aminolevulinate

Topical photodynamic therapy (PDT) of superficial basal cell carcinoma (BCC ) with 5-aminolevulinic acid (ALA) has achieved promising clinical results. However, the efficacy of this therapy for thick BCC is dramatically decrea sed by a limited diffusion of hydrophilic ALA into the tumor. Lipophilic es ters of ALA may enhance their penetration into the lesion. In this randomiz ed, open clinical study, microscopic fluorescence photometry incorporating a li.-ht-sensitive thermo-electrically cooled charge-coupled device (CCD) c amera was employed to investigate the penetration of methyl 5-aminolevulina te-induced porphyrin fluorescence in thick BCC lesions. Both the distributi on pattern and the amount of porphyrins in 32 lesions of 16 patients were s tudied after topical application of 16, 80 or 160 mg/g of methyl 5-aminolev ulinate for 3 or 18 h. A highly selective and homogeneous distribution of m ethyl 5-aminolevulinate-induced porphyrin fluorescence was seen in all lesi ons studied, with much less fluorescence in the adjacent normal skin tissue s. In lesions of up to 2 nun thickness the application of 160 mg/g methyl 5 -aminolevulinate for 3 h showed the highest ratio of porphyrin fluorescence depth to tumor depth (0.98 +/-0.04), thus providing a biologic rationale f or a clinical PDT trial with this regimen. (C) 2001 Elsevier Science B.V. A ll rights reserved.