APOE and actinic keratosis: The histopathological evaluation revealing aggressive, poorly differentiated SCC in both the SKH-hr2 and SKH-hr2+ApoE models, in contrast to the less aggressive SCC found in the Nude mice, and the mix of actinic keratosis, SCC in situ, and invasive SCC in the SKH-hr1 models (Figure 4), provides a microscopic confirmation of the clinical observations.