MAPK3 and neoplasm: To examine the impact of Lkb1 restoration on tumor growth, we generated KT;Lkb1XTR/XTR mice with the Rosa26FLPo-ERT2 (FLPo-ERT2) allele such that Lkb1 expression could be restored within established, Lkb1-deficient tumors upon treatment with tamoxifen (Fig. 1b).