Fluorescence diagnosis in actinic keratosis and squamous cell carcinoma

As different tissue types have distinct capabilities to accumulate protoporphyrin IX, fluorescence diagnosis with aminolevulinic acid-induced porphyrins (FDAP) could be used to discriminate between different types of tissue. Previous results demonstrated higher fluorescence ratios in squamous cell carcinoma (SCC) compared with actinic keratoses (AKs).

The lesional : non-lesional fluorescence ratio of AKs was compared with the ratio of SCC. Other factors influencing macroscopic fluorescence were also assessed, including stratum corneum thickness, which has been demonstrated to account for heterogeneous fluorescence in psoriasis and in AKs.

After 1 week of keratolytic pretreatment, FDAP was performed in 13 patients with 36 lesions suspected for AK or SCC. Biopsies were taken for histopathological diagnosis and measurement of stratum corneum thickness.

No significant differences were found in the fluorescence ratio (lesional : non-lesional skin) between AKs and SCCs, although macroscopic fluorescence was significantly higher in Bowen's disease and micro-invasive SCCs.

There could be a potential applicability of FDAP to differentiate premalignant lesions with a tendency to progress into SCC and squamous cutaneous lesions already progressing into early invasive cancer from other squamous cutaneous (pre)malignancies. The amount of hyperkeratosis, invasiveness and degree of differentiation seem to be responsible for variations in fluorescence intensity.