To determine whether p53 is required for the observed increase in apoptosis and tumor regression following deletion of C/EBPβ, we developed an inducible conditional C/EBPβ-p53 double knockout mouse K14-CreERtam;C/EBPβflox/flox;p53flox/flox (DIKO) (Fig. 5a) in which C/EBPβ and p53 could be spatially and temporally co-deleted in the epidermis and in pre-existing oncogenic Ha-Ras skin tumors. This evidence concerns the gene CEBPB and skin neoplasm.