KRT5 and neoplasm: Similar to progenitors labeled by Krt5-CreER, mice expressing these mutant alleles (LSL-KrasG12D with/without p53flox/flox)22,23, showed high susceptibility to foregut tumor formation from Krt15+ progenitors at regions adjacent to the SCJ (Fig. 2f–j), as compared to regions distant from the SCJ.