Photo-detection using in vivo fluorescence was studied for different stages of chemically induced premalignant lesions and
squamous cell carcinoma (SCC) of the Wistar rat palatal mucosa. It was found that the epithelial dysplasia (numerically expressed in the epithelial atypia index (EAI) of the rat palate, induced by repeated application of the
carcinogen 4-nitroquinoline 1-oxide (4NQO), showed an increase approximately proportional to the duration of the application period. Photo-detection of the lesions using
Photofrin-induced fluorescence was studied with dual-wavelength excitation and the subtraction of images, in an attempt to reduce the autofluorescence. The
Photofrin dose was 2.5 mg kg-1. This was based on a dose-response study for normal tissue damage by
photodynamic therapy (
PDT) in this animal model, because the underlying rationale was to study photo-detection as a method of locating additional (early)
malignancies in patients treated by
PDT. Fluorescence intensities 24 and 48 h after injection of
Photofrin were shown to increase with the duration of 4NQO application and with increasing EAI. For an EAI greater than 15, there was a statistically significant difference (p < 0.01) between the fluorescence signals obtained with and without the injection of
Photofrin. Fluorescence signals of these lesions without the use of
Photofrin (autofluorescence) also showed an increase with increasing stages of epithelial dysplasia of the rat palate. However, the fluorescence signals obtained with
Photofrin were always higher than those of the autofluorescence. From this study, we conclude that photo-detection with
Photofrin has potential in distinguishing chemically induced premalignant lesions and
squamous cell carcinomas from the normal rat palatal mucosa.
Photofrin (2.5 mg per kg of
body weight) certainly adds to the sensitivity of photo-detection, but autofluorescence alone also has promising features for detecting premalignant and malignant lesions of the oral mucosa.