KRAS and squamous cell carcinoma: Although efforts were made to assess the ability of the IFE to form squamous cell carcinomas (SCCs) using IVL-CreERT2 transgenic mice to simultaneously ablate p53 and induce oncogenic KRAS, the results remained inconclusive, as IVL-CreERT2 targets IFE basal cells dedicated to differentiation and not long-term maintained stem cells (Mascré et al., 2012).