Identification of skin lesions through aminolaevulinic acid-mediated photodynamic detection

Abstract

Non-melanoma skin cancer is the most common cancer lesion worldwide. In Brazil, it represents 95% of all skin cancer lesions, and 25% of all tumor types. Early diagnosis allows treatment at initial stages of the disease, improving patient's prognosis. Thus, it is of great importance the development of techniques to aid diagnosis, such as marked fluorescence, which we propose here for early detection of skin cancer lesions. In this study, we use a photosensitive substance, aminolaevulinic acid (ALA), as biomarkers, and analyze its in situ fluorescence response to light excitation. The use of ALA as a biomarker precursor is interesting because it shows selectivity for protoporphyrin IX production/concentration in abnormal cells. Protoporphyrin IX shows high fluorescence yield when excited with UV-blue light. In this study, ALA solutions (at 5% and 10% concentrations) were applied to malignant (basal cell carcinoma) and potentially malignant skin lesions (actinic and seborrheic keratoses), aiming to investigate our ability in detecting and distinguishing them by using this technique. At regular time intervals (15, 30, 45 and 60min), fluorescence images were collected with a prototype system for widefield fluorescence imaging. ALA has provided a marked fluorescence that allowed significant discrimination of normal and tumor. Potentially malignant and benign lesions were all well-identified by their autofluorescence; photodynamic detection did not improve diagnostics. This technique also provided a better delineation of the lesion margins, which is very important for an effective treatment of malignant, potentially malignant and benign skin lesions.