MSI1 and extramammary Paget disease: Furthermore, this study found that MSI1, an RNA-binding protein, is overexpressed in the basal epithelial cells of human EMPD skin, and ectopic overexpression of Msi1 in the epidermal basal layer of mice results in a phenotype resembling human EMPD at histopathological, single-cell, and molecular levels (81), which supports the in situ transformation theory, i.e. keratinocyte-to-Paget-like cell conversion of disease pathogenesis.