Towards a broader use of phototesting in research, clinical practice and skin cancer prevention

Sammanfattning: In western societies, skin cancer incidence has increased dramatically over recent decades, due predominantly to increased sun exposure habits. Ultraviolet (UV) light exposure and individual light sensitivity of the skin constitute two important factors affecting the risk for skin cancer development. Individuals with a heightened propensity to get sunburnt have a higher risk for skin malignancies, and need to protect themselves more systematically from the sun. Individual UVlight sensitivity can be determined either by self-estimation of tendency to burn and tan, as in the Fitzpatrick’s classification, or by use of a phototest. Although phototesting constitutes a considerably more objective method, it is only sparsely used, chiefly due to financial and resource related factors, and is mainly limited to investigation of photodermatoses or dose-management in photo therapy.The general aim of this thesis was to develop and improve aspects of the phototest procedure in rder to broaden the utilisation of phototesting within the fields of research, clinical practice and skin cancer prevention. As a first step, a new phototesting technique, using a divergent UVB beam was evaluated. The principle of the method is to provoke a circular UVB-erythema in the skin, the diameter of which is related to the administered dose and thus the Minimal Erythema Dose (MED). In a test group of healthy subjects, naked eye reading by a trained observer resulted in a more exact, estimation of UVB-sensitivity, compared to traditional phototesting. Since the diffuse border of the provoked erythema was challenging for the untrained observer to read, the need for an objective, bio-engineering technique for test reading was clear. In this thesis, Laser Doppler perfusion imaging (LDPI) has been used. This data also enabled an objective description of doseresponse for the reaction, an outcome not possible in traditional testing. The divergent beam method was also shown to be useful as a model for evaluation of the effect of topically applied substances.In order to broaden the utilisation of phototests in general, a test procedure built on patient performed self-reading of skin tests (a traditional phototest and an irritant patch test) was evaluated. The reliability of these self-readings was shown to be substantial when compared to the control readings of a trained observer.Using the self-reporting procedure, phototesting was evaluated as a tool in primary prevention of skin cancer. The study focussed on sun habits and sun protection behaviour, and also on investigating the impact of different forms of presentation of the preventive information. Results showed significantly higher impact for a personally mediated preventive message than by letterform. For individuals with heightened UV-sensitivity the performance of a phototest led to a greater tendency to adopt sun protection behaviour than for subjects with a lower UV-sensitivity, suggesting that phototesting is a useful way to improve the outcome in terms of preventive behaviours for this group of susceptible, at-risk individuals.Divergent beam phototesting, patient-performed self-reading, and the application of phototesting in skin cancer prevention emerge as three novel, previously little investigated, aspects of phototesting, for which promising results could be demonstrated.