Abstract— The aim of this study was to determine, for regulatory purposes, the potential of MexoryP SX, a broad UVA absorber that also absorbs to some extent in the UVB, to modify the UV radiation (UVR)-induced murine skin tumor development and growth. Skh-hrl mice were exposed to solar-simulated UVR 5 days per week for 40 weeks. Two control groups were irradiated without topical application, three groups received a sunscreen preparation containing either the UVA absorber, MexoryP SX at 5 or 10% concentration, or a filter that absorbs principally in the UVB, 2-ethylhexyl-p-methoxycinna-mate (2-EHMC) at 5% concentration, introduced as a comparator test article. Sunscreen application was performed before UVR exposure 3 days per week and after UVR exposure on the other 2 days (consistent with the design of a standard photocarcinogenesis safety test). Two different weekly UVR doses were administrated: the lower dose was given to one group of unprotected animals, whereas the higher dose was administrated to the other unprotected group and to the three sunscreen-treated groups. The two UVR control groups demonstrated a UVR-dependent response for cumulative tumor prevalence, tumor yield and median latent period. Neither concentration of Mexoryl SX increased the probability of tumor development; consistent with the principles for safety testing, this provides evidence in that it is safe for use in sunlight. Although this study was explicitly designed as a safety test, the results also provide some clues about the efficacy of MexoryP SX in decreasing the probability of tumor development. Topical administration of Mexoryl* SX, at both concentrations, resulted in a 6 week delay in the median latent period compared to high UVR controls, whereas 5% 2-EHMC delayed the median latent periods only by 2 weeks. Tumor prevalence and yield show the same efficacy differences between the two sunscreen ingredients. Tumor protection factors were calculated from these results and found to be equal to 2.4 for the two preparations containing Mexoryl* SX and to 1.3 for the 5% 2-EHMC preparation.