In these mice, administration of tamoxifen (TMX) induces expression of a constitutively active Kras allele (G12D) in chief cells, leading to rapid onset of spasmolytic polypeptide-expressing metaplasia (SPEM) in the corpus within 4 weeks, which progresses to intestinal metaplasia (IM) and mild dysplasia by 12 weeks (19). This evidence concerns the gene KRAS and dysplasia.