KRAS and gastric cancer: Moreover, stable expression of the active form of Ras in the Chief cells of Mist1-CreERT2Tg/+ and LSL-K-Ras(G12D)Tg/+ (Mist1-Kras) mice, which express the active form of K-Ras upon exposure to tamoxifen, can cause gastric cancer with parietal cell loss, spasmolytic polypeptide-expressing metaplasia, and intestinal metaplasia with increased inflammatory responses [69].