TCF7L1 and papilloma: This model for TCF7L1’s role in the development and progression of skin SCC was also supported by the observation made by Chitsazzadeh et al. that expression of the target genes of TCF7L1 are significantly altered not only between normal skin and papilloma/actinic keratosis samples, but also between papilloma/actinic keratosis samples and skin SCC in both human and mice (Chitsazzadeh et al., 2016).