Abstract
INTRODUCTION: Autofluorescence (AF) imaging is a promising non-invasive tool for skin cancer diagnostics. However, AF intensity alone often fails to reliably delineate tumor boundaries due to strong influence from melanin, keratin, vasculature, and surface scattering. AF photobleaching kinetics provide an additional functional contrast linked to endogenous fluorophore content and environment microstructure, but their diagnostic potential in clinical skin cancer imaging remains underexplored. METHODS: To investigate the photobleaching phenomenon, we analyzed AF and photobleaching behavior in 84 histologically confirmed lesions, including 53 sporadic basal cell carcinomas (BCC), 25 BCCs associated with nevoid basal cell carcinoma syndrome (NBCCS, also known as Gorlin syndrome), and 6 squamous cell carcinomas (SCC). Continuous narrow band LED 405 nm excitation for 20 s enabled pixel-wise fitting of exponential decay curves, generating photobleaching parameter maps describing bleaching amplitude (A), decay constant (τ), and residual component (C). RESULTS: Across all tumor types, lesions consistently exhibited lower initial AF, reduced photobleaching amplitude, and faster τ compared to surrounding skin. A key qualitative finding was a systematic mismatch between lesion boundaries seen in AF intensity versus boundaries revealed by A and τ maps, suggesting that photobleaching parameters capture deeper or structurally distinct tissue alterations not visible in steady-state AF emission imaging. NBCCS-associated BCCs showed more homogeneous A/τ patterns than sporadic tumors, while SCC lesions demonstrated coarse, irregular τ distributions distinct from BCC. DISCUSSION: These observations indicate that photobleaching kinetics provide biologically meaningful contrast and may improve non-invasive tumor characterization, with potential relevance for early diagnosis and surgical margin assessment.