To define the role of Cox-2 in oncogenic Ras/p53-mediated tumor formation arising from Krt15+ progenitors in vivo, we bred our mouse model to a conditional knockout allele for Ptgs2 (Cox-2)43 to induce Cox-2 loss of function in our tumor-prone progenitors (Fig. 5d). Here, KRT15 is linked to neoplasm.