Re-expression of Lkb1 in cancer cell lines deficient for Lkb1 has also been shown to result in p53-dependent cell-cycle arrest and enhanced expression of p21.19,20 On the basis of these results, we wondered whether Lkb1 might act to suppress pancreatic tumorigenesis by promoting growth arrest in vivo through transcriptional activation of p21, because preneoplastic pancreatic lesions in Elas-tTA/tetO-Cre, KrasG12V mice have previously been reported to undergo oncogene-induced senescence, as indicated by positive staining for a number of senescence markers.29 Here, TP53 is linked to cancer.