MMP2 and actinic keratosis: Monitoring metalloproteinase activity in the dysplastic epithelium identified in actinic keratosis lesions is a pertinent approach in the more sensitive assessment of malignant transformation potential [18,41], and immunohistochemical studies do not always reflect the exact percentage of immunopositive cells, possibly also due to the fact that MMP-2 expression is regulated by numerous overlapping transcriptional, translational and post-translational mechanisms [30,34,38].