TP53 and osteosarcoma: Recombination of Tp53 in conditional knockout mice driven by osterix-cre recombinase (Osx-cre), a transgene that is actively expressed in more differentiated pre-osteoblasts, results in osteosarcoma with high penetrance (p53 cKO: Osx-cre; p53lox/lox) [28].