Fluorescence staining of oral cancer using a topical application of 5-aminolevulinic acid: fluorescence microscopic studies

Introduction: Topical application of 5-aminolevulinic acid (5-ALA) by means of a rinsing solution has been shown to be a promising new procedure in th e diagnosis of oral malignancies. However, for assessing the reliability of this method regarding fluorescence-guided tumor resections and photodynami c therapy, further information on the distribution and penetration depth of 5-ALA-induced protoporphyrin IX (PPIX) in the tissue is needed. Methods: 2 4 patients suffering from oral cancer were included in this investigation. Biopsies were taken immediately after fluorescence examination and either u sed as native sections for immediate fluorescence microscopic examination ( n = 3) or shock frozen in liquid nitrogen and prepared as frozen sections ( n = 46). Fluorescence imaging and digital image processing were utilized in order to determine the presence of PPIX in regions of various histologies as well as the penetration depth of PPIX into solid tumor. Results: PPIX fl uorescence in the tissue was limited to the epithelium, Both normal and dys plastic epithelium showed PPIX fluorescence. In the stroma, no PPIX fluores cence was found. In some cases (n = 3/4) invasive carcinomas did not show P PIX fluorescence, while the adjacent or overlying normal epithelium was str ongly fluorescent. The penetration depth of PPIX after topical application of 5-ALA was found to be limited to less than 1 mm. Conclusion: PPIX. fluor escence induced by topical application of 5-ALA can be very useful in the d etermination of superficial tumor margins, However, due to the limited pene tration depth there is a risk of not accurately recognizing the infiltratio n depth of solid tumors. The aim of further investigations will be to asses s the tissue distribution and depth of penetration of PPIX following system ic application of 5-ALA, (C) 2001 Elsevier Science B.V. All rights reserved .